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Full text of "Practical Television 1971 November"

SERVICING CONSTRUCTION COLOUR DEVELOPMENTS I «" *" 



VARICAP TUNER 

PANORAMIC MONITOR 



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STRANSISTOR VIDEO CIRCUITS 
TV AUDIO CIRCUITS FOR THE CONSTRUCTOR 
SERVICING THE DEFIANT 9A50/52 SERIES 



flEUI LINE 
OUTPUT 

TRflnSFORITIERS 

ALBA 655, 656, 71 7, 721 £3-75. 890-895, 1 090, 1 1 35, 1 1 95, 1 235. 1 395, 1 435 £5-00. 

ARGOSY. 17K10. 17K11, 17K12, 17K14. 19K17. 17K43£4-00. 

BAIRD. All models price £5-90. From model 600 quote part no. normally found on TX base plate. 

BUSH TV53 to TUG69 £2-00. TV91 to TV1 39 £4-75. (From Model TV1 23 an alternative Square Tag Panel was fitted on Main Bobbin, 

please state if required.) TV141 to TV176 please state part number £4-50. TV75 to TV86 £4-75 (except TV80). 
COSSOR 904 to 957 Rewind £4-50. CT1 700U to CT2378A £5-00. 
DECCA DM1. DM3C (90°), DM4C (70°). DR1 DR2. DR121 £450. DR95. DR100, DR101, DR202. DR303, DR404. DR505. DR606 

£4-50. 
DEFIANT 7P20 to 7609. Prices on request. 

DYNATRON TV30, TV35. TV36, TV37. TV38. TV39, TV40, TV41 etc £4-00. 
EKCO T231 . T284, TC267. T283. T293, T31 1 , T326, T327, T330. TMB272. T344. T344F. T345. TP347. T348, T348F, TC347 TC349 

TC356, T368, T370. TC369. T371 . T372. TP373, TC374. T377A, T393. T394, 433. 434. 435. 436 437 all at £4-00. 503 504 505 

506 £4-75. 
FERGUSON 306T. 308T. 406T. 408T, 416, 436,438, 506, 508, 516, 518. 536. 546. 604, 606. 608. 616 619 636 646 648 725 726 

727. 3600, 3601, 3602. 3604. 3611, 3612, 3614, 3617, 3618. 3619. 3620, 3621, 3622, 3623. 3624, 3625, 3626 3627 '3629. 

£4-00. Jelly Pots, please state colour: red. black or white. 
FERRANTI T1 001,11 002. T1 002/1, T1 004, T1 005, T1023. T1 024. T1 027, T1027F, TP1 026 T1071 T1072 Til 21 TC1 122 TC1124 

T1 1 25, TC1 126 £4-00, 1154, 1155 £4-75. 
G.E.C. BT302, BT342 £3-50. BT454DST-456DST. 2012. 2013. 2014. 2012, 2000OS, 2001 DS 2002 DS £4-50. 
H.M.V. 1865, 1869, 1870, 1872. 1874, 1876. 1890, 1892. 1894, 1896. All models to 2645 £4-00. 
KB OV30. NF70. NV40, PV40. QV10, QV30. RV10. RV20. RV30, PVP20 £4-50. Featherlight £4-50. Chassis No. VC1-VC2-VC3-VC4 

£4 "50. 
M ASTER ADIO 401 3 DST, D500 DST, D507 DST £4-50. 

MARCONI VT1 53. VT1 55. VT1 56, VT1 57, VT1 59, VT1 61, VT1 63. VT1 65, VT1 70. 4611.4800 4801 4803 4615 £400 

MURPHY V310 to 929 £4-75. 

PAM 600S to 5106 £4-00. 

PETO SCOTT. Prices on request. 

PHILCO 1019. 1O20, 2021 £4-13. 1029. 1030, 1035, 1036, 1040 1050 1060 £4-13 

PHILIPS 1 1TG1 90 to 24T301 £5-00. 1 768U to 21 96U. Rewind £4-75 (old unit required) 

PILOT PT450, 452. 455, 650. PT651. P60A, P61 £4-00. 

PYE V200, V400, 200LB. 210. 220, 300F. 300S, 310, 21 OS. 410, 510. 530, 600. 620, 630. 70Q A or D. 710 A or D 830 A or D or LBA 

£4-00. 1 1 U Series, 11 U-P/NO. AL21003. 21 F to 61 . Pan Nos must be given when ordering Pye LOPTS 
R EG ENTONE 197-198. 298. TV402. TV401. TV501 , TV502 £4-50. 10-4-10-6 10-21 17-18 10-12 191 -192 £4-00 
R.G.D. 626, 627, 628, 726, RV202, RV302 £4-50. 51 9-61 9-620-621 C 723 f 4-00. 

SOBELL1000OS, 1002DS, 1005DS, 1010DST, 1012. 1013, 1014, 1018, 1019.1020, 1021, 1032, 1033 1038 1039 £4-50 
STELLA T1 01 1 U to 21 49A £5-00. 
ULTRA 1770, 2170, 1772,1782.2172, 1771,2171,1775.2175,1774,2174.1773, 21 37. 1980c, 1984c. 100c, 200c 2380 2384 1984 

1985. 1986, 1980. 1980a, 1780, 2180. 2181,2183. 2182. 1871, 1783. 6600. 6625. 6626, 6628 6632 6642 etc £4-00 ' 
We can rewind most LOPT £4-75. «.■»««■ 

Post and Packing 26p. C.O.D. 30p extra. 






LINE OUTPUT TRANSFORMER INSERTS ONLY 

BUSH.TV75. TV85. TV92-TV93. TV94-TV95-TV96-TV97. TV98, TV100, TV101, TV103. TV104 TV105 TV106 TV108 TV109 TV110 

TV113,TV115,TV115R,TV115c, £2-75, Complete with heater windings ' ' 

DECCA DR95. DR101. DR202. DR303. DR404. DR505. DR606 £2-75. 

RETURN OF POST SERVICE ON ALL STOCK ITEMS 

CALLERS WELCOME. But to avoid disappointment please phone to check that the items you require are in stock 
All new components inserts are guaranteed for three months from the date of invoice subject to the breakdown being due to faulty 

manufacture or materials. S.A.E. all enquiries. 

Dept. "R" E. J. PAPWORTH AND SON LTD. 
80 MERTON HIGH STREET, S.W.19 01-540 3513 

01-540 3955 



for men of vision 
rebuilt T.V. tubes 





Current types 




17" 


£4-75 21" 


£5-50 


19" 


£5-00 23" 


£6-00 



19" 



Panorama & Rimguard types 

£7-00 23" £9-00 



Twin panel 



£7-50 



23" 



£9-50 



19" 

Cash or P.O. with order no C.O.D. Free delivery 

in U.K. 

Each tube fitted with new electron gun assembly. 

Fully guaranteed for two years against any fault 

except breakage. 

Special terms for Hospitals, Orphanages, Old People's 

homes. 

Manufactured in our own factory backed by over 20 

years' experience in the field of electronics. Callers 

always welcome (by appointment) at 

k.s.t. ltd. 

Providence Mills, Viaduct Street, 
Stanningly, Nr. Leeds, Yorks. 



TV's 



19 NOW £11-95 

TWO YEARS GUARANTEE ALL MODELS 

405/625: 19" £29*95; 23" £39*95 

FREE CATALOGUE 
DAILY DEMONSTRATIONS FOR PERSONAL SHOPPERS 




COMPONENTS 

MUST BE CLEARED 

T ran ii iter Radio Cot**; 25 p 

each. Si«9±* x 6±* X 3±". Post ISp. 
Speakers; 35p. 1\' 80. Brand 
new. Post ISp. 

VHFfFM Tuner*: 93p. 88-108 
mea*. takes EEC8S valve (extra). 
Post ISp. 

Precision Tape Motors: £1-95. 
2Q0,''X5QV. Famous German manu- 
facturer, Post 20p. 
Transistor Gang Condensers: 
10 p. Miniature AM. Post free. 
Modern Gang Condensers: 30p. 
AM/FM or AM only 20p. Post I0p, 
Transistors ISp each. Post free. 
ACI26. ACI28. AFIM, AFI 17. 
OC4S,OC7l.OC8l,OC8[D. 

Valve EL LOO Mp. Only stock in 
the country. 

Pots.: ISp each. Post 5p. D/SW 
500/500 Kfi. D/SW 500/100 Ko. 
D/SW I meo./lOO KO. S/SW 
500 '500 Ko. S/SW 500/1 meg. 



HI-FI VALUE 

I.GARRARD SP25 MK III £1150 
P. & P. 50p. 

2. TEAK PLINTH & TINTED COVER 
£4-95. P. & P. 35p, 

3. SONOTONE 9TAHC CART- 
RIDGE £150. P. & P. 5p. 

BARGAIN PACKAGE— I, 2. 1 
£17-95. P. & P. 85p. 



TV TUBES REBUILT 
GUARANTEED 2 YEARS 



4 



14" £3-93; 17' * 19' £5-93; 
21* & 23" £6-43 

Exchange Bowls carr, 5 5 p. 



TEAK HI-FI STEREO CABINETS £14*95 

ofTrn^C^ l £ T. d W P HrLE l |T f Jc h KS Vi £AST 3i - * """* """ 

DUKE & CO. (LONDON) LTD. 

62U3 ROMFORD ROAD, MANOR PARK, E.12 
Phone 01-478 6001-2-3 Stamp For Ftee List 






High Salary 

A Dream House 

A New Car 

And A Secure Future 

Get into the Computer 
I industry the fast and 
easy way. 

Now for the first time, anybody (no special qualifications 
are needed) can train outside the computer industry for 
an exciting career as a computer operator in only 4 

weeks — and can earn £2,000 -f-+ p.a. 

How? We are the only commercial training organisation 

in the U.K. permitted to use the famous 

'Eduputer'. 

JOBS GALORE! 144,000 new 

operators will be needed over the 

next five years alone. And the 

moment you qualify our 

exclusive computerappointments 

bureau introduces you to 

computer users everywhere. 

This is your big opportunity to get 

out of a rut and into the world's 

fastest growing industry. Find 

out more FREE and 

withoutobligation by 

posting this coupon iji 

TO-DAY. 4|| 





London Computer Operators 
Training Centre 

B89 Oxford House, 9/15, Oxford Street, London, W1 . 
Telephone : 01 -734 2874 

127/131 The Piazza, Dept. B89 Piccadilly Plaza, 
Manchester 1. Telephone: 061-236 2935. 

Please send me your FREE illustrated brochure on exclusive 
Eduputer 'hands on' training for computer operating. 

Name. 






Address, 



.Tel. 



WILLOW VALE ELECTRONICS 

LIMITED 

The Service Department Wholesalers 

Compare aur prices 

e.g. NEW 19" C.R.T's . . . OUR PRICE £7-95 pi us 65P carnage 



> 



Please note: Components are sold in packs, quantities per pack 
are shown under each heading. Prices are per piece of each 

value. 



TUBULAR CAPACITORS 

(S's) 
-001 
■0022 
-0033 
•0047 
■01 
-022 
-033 
•047 



-22 

-47 

•01 

-022 

•047 

-I 

-22 

■47 

-001 



400v. 

600v. 

600/ISOOv. 

600/ISOOv. 

400 v. 

600v. 

600v. 

600v. 

600v. 

600v. 

600v. 

lOOOv. 

lOOOv. 

lOOOv. 

lOOOv. 

lOOOv. 

lOOOv. 

I500v. 



£004 
£0-04 
£004 
£004 
£004 
£0 05 
£0-05 
£005 
£0-05 
£0-10 
£01 4 
£0 06 
£0-06 
£009 
£0-09 
£014 
£019 
£0 08 



WIRE-WOUND RESISTORS 
(S'») 

10 watt rating, suitable for mains 
dropper sections. 
Ohm 

Ohms 



10 
13 
25 
33 

50 

87 

100 

150 

220 

330 

IK 

2-2K 

3-3K 

4-7 K 



£0-09 
£0-09 
£009 
£009 
£0-09 
£009 
£0-09 
£0-09 
£009 
£009 
£0-09 
£0 09 
£0 09 
£0 09 
£0 09 



PULSE CERAMICS (S's) I2KV 

lOOpf 22pf £006 

I20pf 47pf £006 

ISOpf 68pf £006 

250pf £006 
Tubular type for use in Scan 

correction circuits and Line 
Outputs. 



CERAMICS (6's) 



SOOpf 
680pf 
820pf 
lOOOpf 

!500pf 
3000pf 
5000pf 



22pf 
47pf 

68pf 
lOOpf 
I20pf 
ISOpf 



£003 
£003 
£003 
£0 03 
£003 
£0 03 
£003 



BIAS ELECTROLYTICS 



2Smfd 

50m fd 

lOOmfd 

250mfd 

SOOmfd 

lOOOmfd 

lOOOmfd 

2000mfd 

2500mfd 

3000mfd 

SOOOmfd 

25 mfd 

50mfd 

lOOmfd 

250mfd 

SOOmfd 

2000mfd 

2500mfd 



2Sv. 
25v. 
25v. 
25v. 
25v. 
I2v. 
30v. 
2Sv. 
30v. 
30v. 
30v. 
50v. 
50v. 
50v. 
SOv. 
SOv. 
SOv. 
50v. 



(5's> 

£0-07 
£0 08 
£0 10 
£01 5 
£0 19 
£0-30 
£0 30 
£035 
£0-45 
£0-47 
£0-55 
£008 
£010 
£0 13 
£018 
£0-24 
£0-47 
£055 



SUB-MINIATURE 

ELECTROLYTICS (S's) 



SMOOTHING 
ELECTROLYTICS 

Wire ended, 4S0v. working. 

I mfd £0-07 

2mfd £0-08 

4mfd £0-11 

8mfd £01 3 

I6mfc £0-16 

32mfd £0-23 

50mfd £0-25 

8/8mfd £0-19 

8/l6mfd £0-25 

I6/I6mfc £0-26 

!6/32mfc £0-27 

32/32mfd £0-27 

50/50mfd £Q42 

50/50/S0mfd £0-52 



CANNED ELECTROLYTICS 

!00/200mfd £0 63 

I00/400mfd £0-83 

200/200mfd £0-85 

200/200/ lOOmfd £0-95 

200/400/J2m(d £0-95 

IOO/3OO/IO0/16 £0-95 

! 00/400/ 32mfd £0 95 

100/400/64/16 £1-07 



SKELETON PRE-SETS (S's) 

25K Vertical £0-07 

50K „ £0-07 

I00K „ £0-07 

2S0K „ £0-07 

S00K „ £0 07 

1 meg ,, £0-07 

2 meg ., £007 
S00K Horizontal £007 
680 V „ £0-07 
I meg „ £0-07 



I mfd 

2mfd 

4mfd 

5mfd 

8mfd 

lOmfd 

I6mfd 

25mfd 

32mfd 

SOmfd 

lOOmfd 

200mfd 



I3v 

I8v 

I8v 
I8v 
I8v 
I8v 
I8v 
I8v 
I8v 
18v 
I8v 
IBV 



£009 

£0 09 
£009 
£0 09 
£0 09 
£009 
£009 
£0 09 
£0-09 
£0-09 
£0 09 
£0 09 



THERMISTORS (5's) 

Miniature 
THI 



£008 

£0-13 



RADIO/TV GLASS 
FUSES 

I amp, I -5 amp, 2 amp, 3 amp. 
Per dozen £015 



MAINS FUSES 

2 amp, 3 amp, 5 amp, 13 amp. 

Per dozen £0-25 



TERMINAL STRIPS 

2 amp £012 

Samp. £0-14 

15 amp £0-29 



RECTIFIERS 
Silicon Mains (5's) 
WestinghouseSI0AR2 £0-33 

BY 1 27 Milliard £0-26 

BY327 £0-25 



CONTACT COOLED FULL 
WAVE 

75ma £0 60 

I 00 ma £0-70 

ISOma £0-86 



CO-AXIAL PLUGS 

Bakelice top £004 

Egen metal £0-08 

Single point (car radio) £0-10 



SLIDER PRE-SETS (3't) 

I00K £0-08 

I Meg £008 

2-2 Meg £0-08 



JACK PLUGS 

Chrome standard 
Standard 
3-5mm, metal 



£0-20 

£0 15 
£015 



DIN PLUGS (2's) 

3-pin 

5-pin 
Sockets 



£010 
£011 

£0 06 



CARBON FILM RESISTORS 
I watt, I watt and 2 watt. 

The following values are packed 
cartons of six of each Yalue. 



10 

12 

IS 

18 

22 

27 

33 

39 

43 

47 

56 

68 

82 

100 

120 

150 

180 

220 

270 

330 

390 

430 

470 

560 

680 

820 

IK 



ohm 



I-2K 

I-5K 

I 8K 

22K 

2-7K 

3-3K 

3-9K 

4-3K 

4-7K 

S-6K 

6-SK 

8-2K 

I OK 

I2K 

I5K 

I8K 

22K 

27K 

33K 

39K 

43 K 

47K 

56K 

68K 

B2K 

I00K 

I2DK 



I50K 

isoK 

220K 

270K 

330K 

390K 

430K 

470K 

560K 

6S0K 

820K 

IM 

I-2M 

I-5M 

I-8M 

2-2M 

2-7M 

3-3M 

3-9M 

4-3M 

4-7M 

5-6M 

68M 

6-2M 

I0M 

I2M 

ISM 



All the above values are available in 
both { watt. I watt and 2 watt versions. 
*Special for Philips TV's: 

8-2M 2- watt, 23 p per pack. 
Pri ce I watt ■ 1 0, I watt 13,2 watt '23 



DOUBLE DIODE RECTIFIERS 
(5's) 

Bush/Murphy/BRC, etc. 
Line/frame timebases etc. 

3 leg £0 31 

4 leg £0-31 

5 leg £0-31 



VOLUME CONTROLS 

Standard spindle with flat. 

Double pole switch £0-25 

Without switch £0-19 

(One per pack) 
SK, I0K.25K, 50K, I00K, 250K, 500K, 
I meg, 2 meg. 



MOBILE STORES VANS IN LONDON, WEST COUNTRY, WALES AND SCOTLAND 



RECORD PLAYER CARTRIDGES 

ACOS: GP67/2g. High gain general purpose Mono 
GP9I/SC, Stereo-compatible replacement 
GP9I/3SC. High gain version of above 
GP94/ISS. Stereo cartridge 

GENERAL PURPOSE REPLACEMENT FOft TCS's etc. 

High gain, plenty of output (Jap.) 

Stereo version 



£0-83 
£110 
£110 
£1-89 

£0-99 

£1-89 



SERVISOL AND ELECTROLUBE 

PRODUCTS (Nett trade) 

Servisol aerosol can £0-63 nett 

Electrolube 2AX aerosol £0*70 nett 

Servisol Freeiit £0-47 nett 

Electrolube No. I Snorkel £090 nett 

Electrolube 2GX Grease £0-42 nett 

Servisol Aero-Clene for tape heads £0-53 nett 

Servisol Aero-Duster £0-53 nett 



REPLACEMENT 
STYLI 

TC8 £0-23 

GC8 £0-23 






REBUILT AND NEW TUBES-TWO YEARS GUARANTEE 



REBUILT 



17" ® £5-95 



19' 



£5-95 



21 



£7-95 



23 



£7-95 



BRAND NEW 



£6-50 



£7-95 



£9-90 



£10-80 



COLOUR TUBES 
IN STOCK. 
PRICES ON 
APPLICATION 



ALL PRICES ARE METT 



A FEW SAMPLE TYPES, REMEMBER WE STOCK EVERY 
TUBE 



CMEI702, AW43-80, CRMI73, MW43-80. MW43-69*, 
CRMI72*. AW43-38, AW43-09, CM El 705, CMEI703, CI7AF, 
CI7SM, etc. 



CMEI903, CMEI902. CMEI90I, AW47-90, AW47-9I, A47-I4W, 
CI9AH, CI9AF, CI9A. 



CME2I0I, AW53-88, AWS3-89, CRM2I I ; 
20*, MW53-80*. 



CRM2I2*, MWS3- 



CME2303, CME230I, AW59-90. AW59-9I 



♦NEW ONLY. NO REBUILDS 



TWIN 
PANELS 



19' 



CME)906 
A47-I3W 



ON APPLICATION 



23 



CME2306 
A59/I3W 



ON APPLICATION 



EVERY TUBE IN STOCK INCLUDING 12', IS" PORTABLES, PANORAMA & RIMGUARDS. TERMS: CASH WITH 
ORDER. CARRIAGE ANYWHERE IN GT. BRITAIN *5p per Tube 



N 

O 

is 

_ <o < 



OO 



RADIO AND TELEVISION VALVES SMALL SELECTION 

British made valves normally supplied. EVERY TYPE IN STOCK 



DY86/7 

DY802 

EABC80 

EB9I 

EBC90 

EBF80 

EBF89 

ECCSI 

ECC82 

ECC83 

ECC804 

ECHai 

ECH84 

ECL80 

ECL82 

ECL83 

ECLB4 

ECL86 

EF80 

EF85 

EFB6 

EF89 

EFI83 

EFI84 

EH90 

EL34 

EY5I 



EY86/7 

EZ80 

EZ8I 

EZ90 

GZ34 

GYSOl 

PCB6 

PC38 

PC97 

PC900 

PCC84 

PCC88 

PCC89 

PCCI89 

PCC806 

PCF80 

PCF86 

PCF87 

PCF80I 

PCF802 

PCF805 

PCF806 

PCF808 

PCL82 

PCL83 

PCL84 

PCL8S 



PCL86 

PDSOO 

PFL200 

PL36 

PL8I 

PL8IA 

PL82 

PL83 

PL84 

PL302 

PLS04 

PL508 

PL509 

PY33 

PYBI 

PY800 

PY80I 

PY82 

PY83 

PY500 

UABCBO 

UCH8I 

UCL82 

UCL83 

UL4I 

UL84 

UY8S 



CO 



o o 

in in 



CO 



o 

r- 



u 
> 
o 



CO 
CO cc 



u 
a 

DC 
O 



bl 

a 
tr 
o 

^- •#[ 
i- CD 



ALL MAZDA/BRIMAR TYPES IN STOCK. 



TRADE & SERVICE ENGINEERS ONLY SUPPLIED 

Cash with order. 10% MAY BE DEDUCTED FROM THE ADVERTISED 
PRICES EXCEPT FOR NETT ITEMS, C.O.D.. OR TUBES 

All orders must exceed £5 00 in value otherwise postage and packing 
will be charged at 25 p per invoice. Components must be ordered 
in multiples as packed. 

COMPREHENSIVE CATALOGUE listing valves, tubes, L.O.P.T.'s 
components, transistors, including HUGE VALVE EQUIVALENTS 
LIST. I5p in loose stamps, please. 



L . O . P.T.'s 

LINE OUTPUT 
TRANSFORMERS 

ALL MAKES SUPPLIED 

L.O.P.T.'s ONLY AVAILABLE 
FROM LONDON DEPOT 

EXCHANGE UNITS AND 
NEW REPLACEMENTS 

EVERY MAKE SUPPLIED 

(EXCEPT MURPHY OIL-FILLED) 

REWIND SERVICE FOR 
OBSOLETE MODELS 



FRAME OUTPUT, SOUND OUTPUT AND 
MAINS TRANSFORMERS REWOUND 



REMEMBER . . . We are the Service department Wholesalers and supply only the Service 
Engineers' requirements and can therefore carry large stocks, and also we know and under- 
stand your problems regarding getting the right spares QUICKL Y and the RIGHT PRICE. 
HO T-LINE ORDERS: L OND ON 1 -5675400- 2977 , f -579-3582. SOMERSET 045- 84-2597 



4&5THE BROADWAY, HANWELL, LONDON, W.7 

Telephones: 07-567 5400 01-567 2977 07-579 3582 

42 WEST END, STREET, SOMERSET 045-84 2597 



0A2 

OB'2 

OZt 

IAS 

1A5 

1A7GT 

IB3C:T 

11)5 

Jl»i 

1FDL 

108 

IH60T 

1L4 

1LJJ5 

ILN5 

1KSGT 

1ES 

is- 1 

1S5 

HI 

1U5 

3.44 
:<B7 
SDH 
3Q4 
9Q60T 

;j84 

3V4 

r>R4c;Y 

.■5V4G 

nyar.T 

SZ3 

5Z4G 

>i 30L2 

SA80 

»>AC7 

flAOfl 

SAK5 

BAKfl 

liAMfi 

ft AM 8 A 

SAX8 

(IAQS 

UAK6 

BATfi 

OAUB 

tiAVfi 

6AW3A 



BENTLEY ACOUSTIC 
CORPORATION LTD. 

38 CHALCOT ROAD, CHALK FARM, LONDON, N.W.I 
THE VALVE SPECIALISTS Telephone 01-722-9090 

T 



8 AX 4 
fjJiSO 
6BA6 
6BC8 
6BE6 
fiBHfi 
SB J 6 
6BQ; 



039 
13 
020 
060 
021 
43 
039 
22 



003 
126 
78 
054 
031 
19 
0-73 
063 



HBQTA 33 

6BK" 0-79 

fjBRa 

UB97 

GBWtj 

fiflVV" 

6BZ6 

6C6 

6C9_ 

6CB6A 028 

fiCDBG 1 08 

6CGBA 50 

SCH6 0-38 

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All valveB are unused, hoxed, iliicI Htittject to the standard 90-<lpiy giuirant^e. Terms of buslneatj: — 
Cash or cheque with order only. Post/packing 3p per item, subject to a minimum of 9p per order. 
Order* over £5 post/packing free. Same day despatch by urst class mall. Any parcel insured against 
damiLgc in transit for only 3p extra per order. Complete catalogue with conditions of sale price 7p post 
paid. Business hours Mon.-Fri. 9-5.30 p.m. Bats. 9-1 p.m. 

We do not handle seconds nor refect*, which are often described as "New and Tested*' but have a 
limited and unreliable life. No enquiries answered unless 8.A.E. Is enclosed for a reply. 




THE NEW UM4 

COLOURBOOSTER 

UHF/625 LINE 

CAS* PRODUCE 
REMARKABLE 
IMPROVEMENTS IN 
COLOUR AND 
PICTURE QUALITY 
IN FRINGE OR 
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WITH SIGNIFICANT 
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FITTED FLY LEAD-INSTALLED IN SECONDS 
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IVORY PLASTIC CASE 3| x3J x 1 1 CORK BASE 
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Also the M4 DUAL BAND VHF UNIT 

BOOSTS ALL BAND III and ANY SPECIFIED 

BAND I CHANNEL SIMULTANEOUSLY 

NOMINAL GAIN 17-18 DB BOTH BANDS 

PRICES BOTH TYPES: 

£3*75 Battery model or £5-87 Self-contained mains version 

Postage and Packing 13p 

TRANSISTOR DEVICES LIMITED 

6 ORCHARD GARDENS, TEIGNMOUTH, DEVON 

Telephone: Teignmouth 4757 



REBUILT 
TELEVISION TUBES 



17" CS-00 

19" £5-50 



STANDARD TYPES: 

21". £6<50 

23" £7-50 

'PANORAMA' & 'RIMGUARD' TYPES: 

19" £7-00 23" £9*00 

TWIN PANEL or BONDED FACE TYPES: 

19" £7-50 23" £10-00 

COLOUR TUBES: 

19" £25-00 22" £28*00 

25 £30*00 26" £32*00 

(exchange bulbs required) 

Carriage S insurance: 75 p extra for standard tubes; £1-50 extra 
rimguard and twin panel types. £3 extra colour. 

jf Complete new gun fitted to every tube, 

^ Two years' guarantee, monochrome. 1 year colour. 

"-*V Trade enquiries invited. 

^ 14 years' experience in tube rebuilding. 

N.G.T. ELECTRONICS LTD., 

(NU-GUN TELETUBES) 

22 Anerley Station Road, 
London, S.E.20 

Telephone: 01-778 9178 



TELEUISI0I1 

SERVICING - CONSTRUCTION - COLOUR DEVELOPMENTS NOVEMBER 1971 



VOL 22 No 1 
ISSUE 253 



PLAYING AT TELEVISION? 

it is rather easy for those whose main interest is the 
technical side of TV to forget that white television 
engineering has been progressing from 30 feeble lines 
of picture information to 625 lines with colour there is 
another side to television— the actual production of 
programmes. 

Several years ago the field blanking interval on the 
UK 625-line system was increased from 20 to 25 lines 
to allow the insertion of additional vertical interval test 
signals. This was done mainly to satisfy Trade demands 
for colour test signals transmitted continuously through- 
out programmes. If the most enthusiastic television 
broadcast engineers were to have their own way 
however they would probably saturate each and every 
raster with test signals. But whatever one thinks of the 
majority of programmes such a viewpoint is clearly 
wrong : television as we know it is for entertainment 
and information. 

There is a great danger that the engineering depart- 
ments of the BBC and ITA are losing sight of this. With 
the increasing use of unmanned transmitting stations 
for example, engineers are justifying their title by doing 
a great deal more engineering than before and a great 
deal less programme monitoring. The danger here is 
a reduced sense of urgency in correcting faults affecting 
picture quality. 

Not all the lack of purpose can be laid at the door of 
the engineer however and a number of production 
teams are open to criticism. The extent of the improve- 
ment in production techniques since the early days is 
difficult to measure, involving as it does subjective 
assessments. As technical observers however we notice 
an increasing use by the production side of television 
gimmicks for their own sake. The first of these was 
undoubtedly the zoom lens, which for many years 
was used in a very amateur manner. Fortunately that 
fad is now dying out, but other toys are around : slow- 
and stop-motion video playbacks, colour synthesis, 
electronic character generation, chroma -key and so on. 
These are fine when used with discretion, but at 
present they often become a production crew's 
monster toys. 

Television is open to abuse from several directions 
and great care is needed to ensure that its basic 
purposes are not overlooked. 

W. N. STEVENS, Editor 



THIS MONTH 



Teletopics 

Varicap Tuner Panoramic Monitor 

by H. Peters 

ICs for Television— Part 3— RBM Colour 
Decoding ICs by K. T. Wilson 

Simple UHF Aerial Preamplifier 

by Roger Bunney 



Transistor Video Circuits 



by S. George 



20MHz Pulse Sealer/Signal Generator- 
Part 2 by Martin L. Michaelis, M.A. 

Servicing Television Receivers — The First 
Plessey Dual-Standard Chassis 

by L. Lawry-Johns 

Basic Circuits for the Constructor— Part 5 — 
Audio Circuits by J. W. Thompson 

Colour Receiver Circuits — Chrominance Cir- 



10 

14 
16 

18 

22 

26 



cuits 


by Gordon J. King 


31 


Long- Distance Television 


by Roger Bunney 


36 


Service Notebook 


by G.R. Wilding 


38 


TV Test Report 


by E. M. Bristol 


40 


Your Problems Solved 




41 


Test Case 1 07 




43 



THE NEXT ISSUE DATED DECEMBER 
WILL BE PUBLISHED NOVEMBER 22 



© IPC Magazines Limited 1 971 . Copyright in all drawings, photographs and articles published In "TELEVISION" is fully protected snd reproduction or imitation 
in whole or in part is expressly forbidden. All reasonable precautions are taken by "TELEVISION" to ensure that the advice and data given to readers axe reliable. 
We cannot however guarantee It and we cannot accept legal responsibility for it Prices are those current as we go to press. AH correspondence '™" de f 'f ' '™ 
Editor should be addressed to Fleetwav House, Farringdon Street, London, EC4A 4AD. Address correspondence regarding advertisements to Advertisement 
Manager, Fleetway House, Farringdon Street, London, EC4A 4AD. 




BANDS FOR SATELLITE TV 

The recent World Administrative Radio Conference 
convened by the International Telecommunications 
Union has allocated Band VI, ll-7-12-5GHz, for satel- 
lite TV broadcasting in Region 1 which covers roughly 
Europe, Africa, the USSR and Turkey. The confer- 
ence was called to consider the use of frequencies — 
mainly those above 10GHz — that are not at present 
firmly allocated. It looked — as is necessary with the 
current rate of technical progress — some distance into 
the future, going so far as to allocate frequencies for 
space-to-space links, for use for example in satellite- 
to-satellite communications, where the earth's atmos- 
pheric conditions no longer present limitations. 

In allocating frequencies for satellite TV broad- 
casting an official distinction was drawn between 
broadcasting for communal reception for which rela- 
tively low transmitter powers are required and broad- 
casting for reception in individual homes which re- 
quires very much higher power. With this limitation 
in mind the conference accepted the use of the u.h.f. 
TV band between 620-790MHz for satellite broad- 
casting subject to the agreement of those countries 
likely to be affected. Also with this limitation the 
band 2-5-2-69GHz was allocated for satellite broad- 
casting and jt was considered that this will be the main 
band used to provide satellite TV broadcast services 
in developing countries and sparsely populated 
regions where land-based networks would be too 
costly to set up. 

It is proposed to hold a conference of European 
countries to decide how much of the 800MHz com- 
prising Band VI to devote to regional coverage and 
how much to national coverage. The Band is wide 
enough for each W. European country to be able to 
operate four programmes since at s.h.f. very narrow 
beams can be used and channels repeated at appro- 
priate distances. The intention is to use satellite 
channels initially for communal reception, with the 
more powerful satellites necessary for individual home 
reception being introduced later when this becomes 
technically and economically feasible. Terrestrial ser- 
vices in this Band have now been classified as second- 
ary to the satellite broadcasting service to enable 
planning to proceed without restrictions. Once the 
satellite broadcasting plan is finalised individual coun- 
tries will be able to see what frequencies remain 
available to them for terrestrial services. 

Still higher up the spectrum the bands 22-5-23GHz 
(Region 3 only — Asia, Australasia and Oceania), 
41-43GHZ and 84-S6GHz were allocated for broad- 
cast use : the only use likely to be made of these bands 
in the foreseeable future however is for resea/ch and 
development purposes. 



The major companies are quietly undertaking quite 
a bit of research work on s.h.f. TV reception : it seems 
likely that in 10 years or so there will be rich rewards 
for those able to produce reliable systems for use at 
these frequencies. It all shows that there is still a lot 
to come technically in the world of TV. On the non- 
technical side one can foresee battles ahead on the 
use to be made of these new delights when they be- 
come technically possible and how finance is to be 
arranged. (What to do with the fourth u.h.f. UK TV 
service has still to be settled however!) 

The regulations accepted by the World Administra- 
tive Radio Conference come into force on January 
1st 1973. 

FROM THE SETMAKERS . . . 

With the introduction by Decca of a 17in. colour 
model there are now two colour models with this size 
tube on the market. The Decca Model CS1730 is a 
hybrid receiver using 27 transistors, 6 valves and i.cs 
in the sound i.f. and decoder sections. It is a single- 
standard set with a sensitivity of IOOjwV (minimum 
usable signal) and an audio output of 2W. The 
price quoted is £195-50. Decca have also introduced 
a 12in. monochrome single-standard battery/mains 
portable model, the MS1210. 

The latest price quoted for the Thorn/BRC 17in. 
colour set is £182-90. 

Philips have made a further announcement about 
their videocassette recorder. This is to be produced 
in Austria and full-scale supplies of the UK version 
are not expected to become available until towards 
the end of next year. The cassette can be erased and 
used again over 300 times. Philips estimate that sales 
of their videocassette recorder in the UK could reach 
2-5 million by 1980. A rental charge of £1-50 a week 
has been suggested. 

DISPLAY DEVICE FOR MINIATURE TV 

Honeywell are producing lin. square 0-005in. thick 
ceramic slices capable of storing over two billion data 
bits: the electrical properties of these chips are said 
to make them suitable for use as the display device in 
a miniature TV set. 

STATE OF THE TRADE 

Sir Jules Thorn, chairman of Thorn Electrical Indus- 
tries, commenting on the 1970-71 results says: "The 
1970s should see the greatest expansion ever achieved 
in the radio and television industry." Total home and 
export sales of Thorn/BRC products in 1970/71 rose 
by nearly 50% compared to the previous year with 



a substantial increase in profits. The experience of 
Thorn /BRC is that the high level of colour TV sales 
has not affected their sales of black-and-white re- 
ceivers : in fact Thorn had a record year for sales of 
both monochrome and colour sets. On the rental side 
the number of colour subscribers to the group's 1,000 
shops more than doubled during the year. Concern 
is however expressed about the increasing competition 
from the Far East. 

The radio and television division of GEC also had 
a record year due to much higher colour TV set sales. 
For GEC monochrome set sales were marginally 
lower though in both categories GEC claims to have 
ended the year with a larger share of the market. 

BREMA reports that present indications are that 
most setmakers will find the production of dual- 
standard sets uneconomic by the end of 1973 though 
a small but declining demand will continue for some 
years in those areas and pockets unable to receive 
u.h.f. It is estimated that by the end of this year 85% 
of the population should be able to receive all three 
programmes on 625. 

The latest BREMA delivery figures, for July, show 
a sharp rise in deliveries of colour sets to 69,000, easily 
the highest monthly total yet. The "mini-budget" in 
which controls were eased and tax cuts made affected 
only the second half of the month. Monochrome de- 
liveries rose from 90,000 in June to 1 10,000. 

Some recently released figures on US radio and TV 
imports make sobering reading however. In 1970 
91% of the radio sets sold in the USA were imported 
while 51% of the monochrome TV receivers and 
18% of the colour receivers sold were imported. With 
the 10% US surcharge in effect Far Eastern exporters 
will be glancing at other potential markets. The UK 
TV industry may be booming just now but it doesn't 
look as jf a sellers' market will be able to develop. 



UP-C0NVERTERS FOR CATV SYSTEMS 

With the phasing out of dual-standard receiver pro- 
duction, what to do if you have a v.h.f. wired TV 
distribution system? With this coming problem in 
mind BREMA have recommended the use of an "up- 
converter" which accepts 625-line v.h.f. signals from 
the network and converts them back to u.h.f. so that 
a conventional single-standard receiver can be used. 
Teleng have now introduced such a unit, called the 
"Super verier". This is mains powered and provides 
an overall gain of 4dB. For optimum performance 
the input signal level is l-2-2-5mV r.m.s. peak: if the 
signal level is above this it may be necessary to use 
an attenuator between the TV system outlet and the 
converter to prevent interference from unwanted pro- 
grammes. Teleng say the unit should be mounted in 
a position where the temperature is stable and good- 
quality coaxial cable used. 

BREMA comment that they expect this technique 
to be used increasingly in the future. They also expect 
that the majority of new coaxial distribution systems 
will supply signals to subscribers at u.h.f. 

UHF SERVICE EXTENSIONS 

The IT A has now brought into service three new 
main u.h.f. transmitters and the first two of its u.h.f 
local relay stations. The new main transmitters are: 
Craigkelly, Fife, carrying Scottish Television pro- 
grammes on channel 24 (250kW e.r.p.); Stockland Hill 



near Honiton, Devon, carrying Westward Television 
programmes on channel 23 (250kW e.r.p.); and Cald- 
beck near Carlisle, carrying Border Television pro- 
grammes on channel 28 (500kW e.r.p.). A group A 
receiving aerial horizontally polarised is required for 
all these transmissions. 

The first IT A u.h.f. relay stations are at Pen die 
Forest, Lancashire, carrying Granada programmes on 
channel 23; and Wharfedale, Yorkshire, carrying 
Yorkshire Television programmes on channel 25. A 
group A receiving aerial vertically polarised is required 
for both these transmissions. 

Both BBC- 1 and BBC-2 are now being transmitted 
by the BBC Wharfedale relay station: BBC-I is on 
channel 22 and BBC-2 on channel 28. The Heathfield 
(East Sussex) main station is now transmitting BBC-1 
on channel 52 (group D receiving aerials horizontally 
polarised are required) and the BBC has now brought 
into operation its Caldbeck, Cumberland, transmitter 
with BBC-2 transmissions on channel 34 (receiving 
aerial group A with horizontal polarisation). 



ADJUSTABLE-TEMPERATURE SOLDERING IRON 

An adjustable-temperature, thermostatically-con- 
trolled soldering iron, the Oryx 50, has been intro- 
duced by W. Greenwood Electronic Ltd., 21 Germain 
Street, Chesham, Bucks. The iron can be simply set 
to any temperature between 200-400 C C without chang- 
ing the bit and the settings are accurate to ± 2%. 
Tip temperature variations during soldering are said 
to be negligible and temperature changes can be made 
in seconds while the iron is on. The Oryx 50 will 
operate at much lower temperatures than conventional 
uncontrolled irons. A long-life iron-coated bit is fitted 
as standard and there is a range of 11 bits — long-life 
or copper-nickel plated to choice. The iron is rated 
at 50W, weighs 2|oz and heats up in 45 sees. There are 
12, 24, 50, H5 or 210-250V a.c. versions. 



BINDERS 

We have been asked by our Binding Department to 
point out that the binders which are available from 
them at 75p to hold a year's copies of Television are 
supplied either blank or with the volume number 
printed on the spine. When ordering a binder please 
state whether you want the binder blank or with the 
volume number — and which number in this case — 
printed on the spine. The address to which orders 
should be sent is: Binding Department, IPC Maga- 
zines Ltd., Carlton House, Great Queen Street, 
London WC2. 



DX-TV PAMPHLET 

Judging from the number of readers who wrote in to 
Roger Bunney recently for a copy of his DX-TV pam- 
phlet there is a very considerable interest in the sub- 
ject of long-distance television reception. He quickly 
ran out of his first batch of pamphlets and has had 
to run off a further supply : our apologies to all those 
who were kept waiting while this was being done. 
Any other readers who would like a copy of the 
pamphlet, which gives details of the various modes of 
long-distance TV signal propagation, the standards in 
use and advice on how to receive DX-TV signals, 
should write in to us enclosing a postal order for 15p 
made out to Roger Bunney. 



8 

It was obvious that a race was on between BBC-1 
and ITA to be first on the air with our local duplicated 
services and in the true workshop -tradition heavy odds 
were placed. What we needed was a simple device to 
monitor the whole band continuously : the rig about 
to be described does the job very well. It uses a 
varicap (variable-capacitance diode) tuner, an i.f. strip 
and an oscilloscope and displays a trace covering the 
entire u.h.f. band simultaneously. Once the race was 
over (it was a dead heat!) the unit was tidied up and 



r 



'ETERS 





VARICAP TUNER^. 

PANORAMIC MONITOR 



put to a number of uses which will be described later 
on. 

The Varicap Tuner 

In case you have yet to meet one, a varicap tuner 
(see Figs. 1 and 2) is a tuner with the four rotating 
gang -cap actor sections replaced by four variable- 
capacitance diodes. By applying a reverse voltage to 
all these diodes together they can be made to tune the 
tuner from channel 21 to channel 68. Usually the 
voltage needed to tune channel 21 is about +1V and 
that required to tune channel 68 about + 30V, This 
variable voltage is usually taken from a variable 
potentiometer network fed by a well-stabilised 30V 
line and the diodes themselves are carefully selected 
in matched groups since there can be no compensation 
for tracking errors by bending the end vanes as. in 
mechanical tuners. 

The other supplies normally connected to the tuner 



are about + 12V, 10mA l.t. for the transistors and a 
forward a.g.c. voltage to the base of the r.f. transistor. 
In our case we are concerned with only u.h.f. but 
v.h.f, varicap tuners are also made: these have an 
extra pin connection taken to a second group of vari- 
cap diodes inside the tuner which act as switching 
diodes to determine whether the tuner works on Band 
I or Band III, switching being accomplished by con- 
necting the extra pin to the 12V line. Various tuners 
— all u.h.f. — gave satisfactory results in our circuit. 

Panoramic Monitor Circuit 

The panoramic monitor circuit (see Fig. 3) has 
been kept intentionally vague so that you can adapt 
it to your own existing gear. The oscilloscope should 
be capable of delivering a 0-30V sawtooth from its 
"X Out" socket and have a Y sensitivity of IV /cm. 
or better. Sweep speed can be 50Hz but is not critical. 

The i.f. strip used can be almost any working unit. 




Fig. 1; Typical varicap tuner circuit. L2, C2 form an untuned input circuit; DJ, L1 are a series trap tuned to 79MHz (twice 
the i.f.) high for good image rejection; D2, L3 and D3, L4 form a tuned bandpass r.f. coupiing; D5, L6 are the local oscil- 
iator tuned circuit; L5 provides local oscillator feedback; L7 is the primary of the first i,f. transformer; D4 is a compensating 
capacitance-diode to maintain even oscillator output; CI, C3, C4 and C5 are tracking capacitors; Tr1 is an r.f. amplifier 

with a.g.c. and Tr2 the mixer/ oscillator. 



Fig. 2: Pin connections of common varicap tuners. 
(a) and (b) European u.h.f. types in current UK sets; 
(c) European v.h.f. type in current UK sets; (d) 
Mallard u.h.f. type ELC 1043— the ELC1042 v.h.f. 
type is similar but has an extra pin for band switching 
to which 12V is applied to switch to Band HI. 

Mui/ard varicap tuners can be obtained from 
Gurney's Radio, 91 The Broadway, Southall, 
Middlesex. A suitable i.f. strip was featured in our 
July 1971 issue. 



Tune IF 



LT 12V C3 
Ose LT 12V 

9) ® e 

Control 

Wits 

(a) 




Control 

volts- 

• e 

LTI2V 
Osc 



e 

LT52V 



fB 



AGC 



Also gives extra IF g*ln (or UHF tuner 



® ® 
LT Contra! 
t2V- volts. 



Its/* 



LT IF In 
12V from 
UHF tuner 



I F out AGC 



Mxer collector- not used 



(c) 



Osc 
LT 



■ 

Control 

volts 



® ® ® fr 
,GC LT / I 

.. r/-K 

A* In 
it in 



Apply 12V tor Band III A* In 



lb] 



w 



• o ® 

LT 12V A6C 
switching 

_ pin an VHF 

version ELC1042 



The output is taken from the vision detector diode 
after the i.f. filter. Provision must be made to dis- 
connect the a.g.c. and use a manual variable bias 
supply. A clue as to what is needed here is to be 
found in the alignment instructions of the strip as 
the a.g.c. is normally clamped to a fixed bias during 
alignment. 

Figures 3(a) and (b) give alternative methods of 
obtaining the transistor supply for the tuner from 
a transistorised i.f. strip. If you have an i.f. strip 
with a positive l.t. rail of 18-20V follow Fig. 3(a); if the 
l.t. rail on the i.f. strip is negative follow Fig 3(b). The 
tuner is wired conventionally into the i.f. strip. Most 
tuners require +12V and this can be dropped from 
the 18 -20V i.f. supply using a iW 820fi (approxi- 
mately) carbon resistor. No a.g.c. is to be applied to 
the tuner so the r.f. transistor is biased on to a 
maximum gain condition with about 2mA of emitter 
current by Rl and R2 (1.2kft and 8.2k^ respectively). 

Working Principle 

The normal control voltage to the varicap diodes 
is replaced by the 0-30V sweep from the oscilloscope. 
Thus the tuner is running from channel 21 right 
through to channel 68 at sweep rate and in this way 
displays the entire band on the 'scope trace. This 
sweep could be a direct connection but for added 
versatility two potentiometers have been fitted in the 




Varicap tuner (7* Input -> 

% Control ™** 

AGC 12V LT volts IF out -20V LT i 

L T.-1 ■ i— f- 



100p_ 
>820 



Teili ' 

Tcm 



'See 
text 



2Sk>*-! f\AAr- 

> lOuFet. 100k 



Oscilloscope 



X X 

In E out 

OOOfOOO " 



Sweep 
"amplitude 



IMF 

2S0' 



1 



(h| 

Fig. 3: Panoramic monitor circuits, (a) for use with an 

18- 20V positive l.t. supply and (b) for use with a ~2QV 

negative l.t. rail 



feed. One varies the amount of sawtooth applied and 
is used as a trace expander. The other sits the saw- 
tooth on a steady d.c. derived from the l.t. supply 
and this acts as a shift control. Used together these 
controls enable the user to zoom in on any particular 
section of the band for a closer look. A I/*F paper 
capacitor acts as d.c. block between the 'scope X 
outlet and the shift network. If you intend to use a 
live chassis i.f. strip or to run the tuner from a nega- 
tive i.f, rail you must also fit a suitable blocking 
capacitor in the return lead. 

Constructional Notes 

The layout is not critical: tuner, resistors, potentio- 
meters — which may be presets — will all fit on a piece 
of veroboard 3 x 2in, Provided the l.t. polarity is 
right the tuner etc. can be mounted on the i.f. board 
itself. The tin case of the tuner has been negative in 
all tuners so far encountered. 

The 'scope X output can be checked for adequate 
sweep by feeding "X out" into "Y in" with the sen- 
sitivity set at lOV/cm. You should see a diagonal line 
3cm. high. Ensure that this sweep is not damped by 
the lOOkH sweep control. If the 'scope is unable to 
deliver the right X output use a 30V p-p 50Hz a.c. 
mains sweep both for the tuner and the 'scope. 

The i.f. strip should be peaked for the narrowest 
bandwidth consistent with stability. The narrower you 
tune it however the slower you will need to sweep or 
you may not receive the fine vertical line which rep- 
resents a transmission. A useful unit can be made 
from a dual-standard i.f. strip which gives three dif- 
ferent bandwidths by simple switching: 625 vision 
provides a broad square-topped pulse for ease of 
identification; 405 vision alignment separates adjacent 
sound and vision carriers and is a good general- 
purpose alignment; 405 sound (38.15MHz) channel 
gives a really narrow sweep bandwidth for looking at 
finer points of sound /vision ratio etc. 

Calibration can easily be done using the third har- 
monic of a Band III v.h.f. generator, using your local 
station as a known starting point. For example 
channel 33 is 567MHz and a generator set to 189MHz 
(Band III channel 8) will beat against this with its 
third harmonic. The scale of the sweep is non-linear, 
stretched at channel 68 and cramped at channel 21. 

Applications 

The device in its crudest form in invaluable for 
service departments and DX enthusiasts. Periods of 
reduced power during test transmissions are not only 
.spotted straight away but can be measured reasonably 
accurately. 

Whilst we were monitoring our duplicated services 

— continued on page 15 



10 




PART 3 



K. T. WILSON 



RBM COLOUR DECODER i.C.s 



The i.c.s we will be looking at this month have been 
developed by Rank -Bush- Murphy for use in the de- 
coding sections of colour receivers : they are made 
for Rank-Bush-Murphy by the Plessey Company. 

SL90I Demodulator and RGB Matrix 

The SL901 has been used in Rank-Bush-Murphy 
colour sets since late 1968 to carry out chrominance 
signal demodulation and colour-difference /luminance 
signal matrixing, providing RGB outputs which after 
further amplification are used to drive the cathodes of 
a shadowmask tube. It is encapsulated in a twenty- 
pin flat pack with tabs for heatsinking and mounting 
and contains the equivalent of 27 transistors, two 
diodes and 31 resistors. It requires a supply voltage 
of + 18V, taking a typical current of 32mA. 

A block diagram showing the functions performed 
by this i.e. is shown in Fig. 1. The Y (luminance) 
signal is generally fed in at pin 10 to an emitter- 
follower whose output is available at pin 9. If — as 
in RBM chassis— brightness control pedestal pulses 
are to be fed into the i.e. these, along with the output 
at pin 9, are fed to a second emitter-follower via pin 
8. If these pulses are not to be fed into the i.e. the 
luminance signal can be fed directly to pin 8 via a 
blocking capacitor. The output from this second 
emitter- follower is then fed internally to the colour- 
difference/luminance signal matrixing stages from 
which the RGB outputs are derived. These are avail- 
able at pins 13, 12 and 7 respectively. (The RBM 
brightness control pulse system was described in the 
September 1971 instalment of Colour Receiver 
Circuits.) 

The V and U chrominance signals from the PAL 
delay line circuit are fed to balanced synchronous 
detectors at pins 18 and 3. The demodulated V 
(R— Y) signal is fed to the red matrix and also to the 
matrix which recreates the G— Y signal; likewise the 
demodulated U (B— Y) signal is fed to the blue and 
the G— Y matrices. Pins 15, 6 and 14 enable external 
controls to be connected to preset the levels of the 
R— Y, B— Y and G— Y signals. Second-harmonic 
rejectors are also connected to these pins. The 
balanced synchronous detectors require push-pull 



reference signal inputs and these are fed in at pins 
16, 17 and 5* 4. Pins 1 and 2 are connected to an 
internal temperature-compensated bias system and 
are decoupled by external capacitors. 

Internal Circuit 

The complete internal circuit of the SL901 is shown 
in Fig. 2. The two luminance emitter-followers are at 
the extreme left-hand side. Tr8, Tr9 and TrlO form 
the blue matrix and output section. The luminance 
signal is fed to Tr9 and the demodulated B— Y signal 
to Tr8 : the resultant blue output signal is taken from 
TrlO emitter. Similar circuits are used to obtain the 
red and green output signals. 

Each balanced synchronous demodulator employs 
seven integrated transistors, Trl-Tr7 being the B— Y 
demodulator. Readers will notice the similarity be- 
tween this and the detector circuit described in Part 1 
of this series. There are again three long-tailed pair 
circuits, Trl and Tr2, Tr3 and Tr4, Tr5 and Tr6. 
Fixed bias is applied to the bases of Trl , Tr4, Tr6 and 
Tr7; the U chrominance signal is applied to Tr5 base 
and the U reference signal in push-pull to the bases 
of Trl and Tr2/3. The demodulated B-Y signal 
developed across Rl is fed to Tr8 in the blue matrix/ 
output section. An output in opposite phase is taken 
from the collectors of Trl and Tr3 to the G— Y 
matrix which consists of R2 and R3. 

External Circuitry 

Figure 3 shows typical external circuitry for the 
SL901 when used in a PAL receiver (this i.e. can also 
be used in NTSC receivers). Transformers with 
centre-tapped secondaries (earthed to signal by 0.1 juF 
capacitors) provide the push-pull reference signal in- 
puts required by the balanced synchronous demodu- 
lators. The delayed and undelayed chrominance 
signal (U+V) is separated into the U and V com- 
ponents in the usual adding and subtracting matrix 
and the outputs are balanced by means of the two 
lOkQ potentiometers. A bias voltage from pin 2 of 
the i.e. is applied to the centre-tap of the add /subtract 

To colour- difference si gnat gain 
presets and harmonic rejectors 



V chroma m lB fc u balanced 



input 



V reference 
sub carrier 



16 1 



Bias and 
decoupling 



U reference 
subcarrier 



Input 



Input 

■HSL* 

ffrfi I 



Bias 
network 



,3 m U balanced 
demodulator 



G- Y 
matrix 



V input 



Emitter- 

follower 

9 t il 

•— •» a 



-* R 
matrix 

and 
P». output 



G 

matrix 

and 

output 



~j matrix 7°"' ^ 

Emitter- 1_ I oj'tpu, Output 
follow ^^ L.Jgl" 



Ft 

output 



6 
output 



Output 



'Brightness control pulse and 
alternative Y Input (see text) 



fig. 1: 



Block diagram of the SL901 chrominance de- 
modulator and RGB matrix i.e. 



11 



Lumin*Kt Mh g-Y 







Internal circuit of the SL901 demodulator! matrix i.e. 



transformer winding. This pin is decoupled by an 
0.1, wF capacitor to the same earthing point to which 
pin 19 is connected. The separation of input and 
output earthing points is fairly common in i.e. work 
and must be carefully observed. The luminance signal 
is a.c. coupled to pin 10 along with a bias of 2-6 V. 
The output from pin 9 is fed to pin 8 along with the 
brightness control pulses. A bias voltage from pin 1 
is also fed to this pin. 

The RGB outputs are taken via low -leakage elec- 
trolytic coupling capacitors — 6.4/aF in the RBM 
chassis — and preset drive controls to the external 



Fig, 3 (right): External circuits for use 
with the SL901. The usual PAL delay 
fine circuitry separates the U and V 
chrominance signals which are then fed 
into the i.e. at pins 3 and 78 respectively. 
The demodulators require balanced 
reference input signals which are fed in 
at pins 16 and 17 (V reference signal) 
and 4 and 5 (U reference signal). The 
luminance signal can be fed in at pin 
10 orpin 8 (see text). 



2nd harmo 
rejection 




UndeUytd 
chroma Input 
lU + Vl 



4 i" Wv * 



RGB output amplifiers. The networks attached to 
pins 6, 14 and 15 are for gain adjustment and second 
harmonic rejection in the three colour-difference sig- 
nal channels. Rejection is carried out by series 
resonant traps which short out signals at the second 
harmonic of the subcarrier frequency. The source of 
this harmonic is the switching action of the demodu- 
lators : a good comparison is the 100Hz hum in a full- 
wave rectifier operating from a 50Hz supply. 

As with any i.e. there is a fairly large gain tolerance 
for the amplifying stages. The maximum gain toler- 
ance of the SL901 is ±25% and the contrast and 
colour controls in other parts of the receiver must be 
able to take up this variation. Similarly the colour 
drive controls at pins 7, 12 and 13 should be able to 
compensate for a possible 1 6 % variation between any 
two of the output signals. The presets used at pins 
6, 14 and 15 to set the gains of the three colour- 



Brightness control 
pulse input 

difference signals should be able to compensate for 
gain differences of ±16%. 

The SL90IB 

In the latest series of RBM single-standard colour 
models the SL901 has been replaced by the SL901B. 
This is different externally in being encapsulated in a 

24-pin flat pack. 

The SL9I7A 

Along with the SL901B the latest Rank-Bush- 
Murphy decoder uses a second i.e. into which most 
of the rest of the decoder circuitry has been in- 
tegrated. This i.e., the SL917A, is also encapsulated 
in a 24-pin flat pack and carries out the chrominance 



12 



Chroma input 



n* mil fmt 



Input from 
envelope detector 



4UV +11V +SV +2V 

Mil 



Burst gating 
pulses 



7 19 9 3 



Chroma 
amp 






Burst blanking 

and gating 



DC 

a rip 



1 1 



Gain 
control 



Colour 
killer 



Chroma 
amp 



Phase 
switch 



Bistable 
1 



Burst 
amp 



PAL V 
switch 



Idant 
switch 



Emitter- 
follower 



Reference 
amp 



Emitter- 
foltower 



Burst amplitude Burst output to passive Pulses to Input from 

con trot su be airier regenerator circuit, trigger passive subearrier 

Also to envelope detector bistable regenerator circuit 
And ACC rectifier 



/7T77 



Chroma output 



Switched V subearrier 



V subearrier phase setting coil 



U subearrier 
(via phase adjusting network) 



Fig. 4: Block diagram of the SL977A chrominance and burst signal processing i.e. 



and burst signal processing operations, providing a 
chrominance signal output to drive the PAL delay- 
line circuitry and the U and V reference subcarriers 
required by the demodulator/ matrixing i.c. The 
SL917A contains the equivalent of 51 transistors, five 
diodes and 50 resistors. The operations it carries out 
are indicated in the block diagram shown in Fig. 4. 
Before describing these operations however we must 
briefly outline one or two techniques not previously 
described in these pages used by RBM in their single- 
standard colour sets. 

Passive Subearrier Regenerator 

The main difference between the RBM single-stan- 
dard and most other UK decoders lies in the use 
made of the burst signal. Instead of being amplified 
and fed to a phase discriminator controlling the phase 
and frequency of a crystal oscillator — the usual tech- 
nique — RBM use the burst signal directly to generate 
the reference signal in what is known as a passive 
subearrier regenerator. Briefly what happens is that 
the bursts are amplified and the PAL alternate line 
burst swing then removed in order to obtain a con- 
stant-phase burst signal. This is then fed to a 4.43MHz 
crystal filter circuit: the crystal has an extremely 
high Q and oscillates throughout the line period until 
the next burst arrives. This signal after amplification 
is then used as the reference subearrier required for 
the synchronous demodulators. 

Looking at this in a little more detail, the burst 
occurs once each line and thus consists of a carrier 



Crystal filter response 
Sidebands spaced at T5-625kH 






To subearrier 
frequency -1kHi 



^Additional sidebands at 7-8 kHz 
created by PAL switching 



To subearrier 
.frequency 41 MHz 



Fig. 5: The burst signal consists of 10 cycles of the sub- 
carrier occurring once each line. It is thus equivalent to 
a 4-43MHz carrier modulated by a pulse at line frequency, 
giving the spectrum shown above. Sidebands occur at 
half line frequency, i.e. 7-8kHz, as well because of the 
burst alternations in the PAL system. 



modulated by a pulse at line frequency. The fre- 
quency spectrum is shown in Fig. 5: in addition to 
the wanted carrier there are sidebands at 15.625kHz 
intervals. The PAL burst alternations also modulate 
this signal so that sidebands appear at 7.8kHz in- 
tervals also. The action of the crystal filter is to 
remove the sidebands so that the wanted carrier only 
is obtained. Crystals with a response sharp enough — 
as shown — to remove the 15.625kHz sidebands are 
readily available. To obtain sufficient sharpness to 
remove the first pair of 7.8kHz sidebands as well is 
less easy to do economically. It is for this reason that 
the PAL alternating bursts are converted to a con- 
stant-phase signal prior to being applied to the crystal 
filter circuit. 

The basic passive subearrier regenerator circuit 
is shown in Fig. 6. The bursts, after the usual 
gating and amplification, are fed to a tuned circuit 
LI, CI which drives the crystal. The crystal behaves 
as a series acceptor circuit with extremely sharp 
tuning so that only the 4.43MHz subearrier appears 
at its output. Circuit stray capacitance and the 
capacitance formed by the crystal material with the 
two connecting electrodes present a problem because 
this capacitance, being in parallel with the crystal, 
effectively bypasses it. Thus without neutralisation 
sideband components would appear at the output. 
Neutralisation is effected by centre-tapping LI so 
that outputs in opposite phase are obtained at each 
end. The neutralising trimmer is then adjusted to be 
of value equivalent to the stray capacitance across 
the crystal so that off-resonance signal components 
cancel, the output obtained from the circuit being 
that due to the crystal alone—a pure 4.43 MHz sine- 
wave. 

Signal Paths in the IC 

Returning to Fig. 4 we see that the chrominance 
signal undergoes the usual processing — the signal path 
is shown across the top of the block diagram. The 
chrominance signal — taken from the chrominance i.f, 
strip in the RBM chassis — is fed in at pin 14. After 
initial amplification the bursts are blanked out, gain 
control and colour killing actions are then under- 



13 



Burst 



input 



Stray capacitance 
across crystal " 



—II 



ci 

|27p 



^ h 



4-43MH2 



1 
I 



4-43MHZ 
crystal 



T&H& 



Neutralising trimmer 
' 2-10p 



6-43 MHz CW reference 
* signal 



Basic passive subcarrier regenerator circuit. 



u lo*) 




(line 2) 



225* 

(a) Received bursts 




Ibj 90* shitted bursts 



Fig. 7: The two burst feeds to the phase switch, (a) 

Received bursts, (b) Bursts shifted by the action of the 

90° coif to swing ± 45° about the V axis. 



Correct phase switching 
V 



Incorrect phase switching 
V 



Received burst 
V 



-V 

90* shifted burst 
V 




B 90* shitted burst 



Received burst 



Fig, 8: When the phase switching is correct a constant- 
phase burst signaf output is obtained; when the switching 
is incorrect no output is obtained because the bursts on 
alternate lines cancel. 

taken and after further amplification a chrominance 
signal of amplitude suitable to drive a PAL delay- 
line circuit is obtained at pin 18. The colour control 
is linked to the final amplification section via pin 16, 
The burst gating /blanking section also provides 
two gated burst feeds to the phase switch, One of 
these carries the normal PAL burst signal, alter- 
nating ±45 c with respect to the — U axis as shown 
in Fig, 7(a). The other feed consists of a signal phase 
shifted by 90° as a result of the action of the 90° 
coil connected to pin 11 (this coil tunes with the 
internal capacitance of the i.e.). As a result of this 
phase shift the bursts in this feed swing ±45° with 
respect to the V axis as shown in Fig. 7(b). The 
purpose of the phase switch is to remove the PAL 
burst phase alternations so that a constant-phase 
output is fed to the burst amplifier and hence via 
pin 6 to the passive subcarrier regenerator previously 
described. If the phase switch is correctly syn- 
chronised it will on line 1 pass the 135° burst shown 
at A in Fig. 8 while on the next line it will pass the 
90° shifted burst shown at B. These outputs add. 




"The TV man came to straighten the picture." 



If on the other hand the switch is incorrectly syn- 
chronised it will pass the 90° shifted burst shown at 
C on line 1 and the 225° received burst shown at D 
on the next line: this time the outputs, being in 
opposite phase, cancel. 

The subcarrier produced by the external crystal 
circuit is fed back into the i.e. at pin 2, A reference 
amplifier section provides two outputs. A subcarrier 
for the U synchronous demodulator is obtained via 
an emitter-follower at pin 22 : its phase is adjusted 
by an external tuned circuit. The subcarrier for the 
V synchronous demodulator is obtained at pin 20 via 
a 0-180° PAL switch and an emitter-follower. Phase 
adjustment of the V subcarrier is carried out by an 
external coil connected to pin 21. The PAL V switch 
is driven by an integrated bistable circuit which also 
drives the phase switch so that the two operate in 
synchronism. The bistable is triggered in the usual 
way by pulses derived from the line output stage. 

The only actions which we have not covered so 
far are the ident feature and the colour killer which 
are operated from the same source. This depends 
on the burst phase switching. We have seen that 
when this is correct the output signals obtained from 
the phase switch add while if it is incorrect they 
cancel. We get an output from pin 6 therefore only 
when the bursts are present and the phase switching 
is correct. An envelope detector connected to pin 6 
will thus give an output when the bursts are present 
and the switching is correct and no output otherwise. 
The output obtained from this detector is fed in at 
pin 4 to a d.c. amplifier and is used as the colour 
killer turn-on bias and as a bias to switch on the ident 
switch. A short time-constant is required in the ident 
switch circuit: the usual action then occurs, the 
bistable missing a count if its initial switching — 
which starts when the circuit is first powered — is not 
in the correct sequence to suit the transmitted PAL V 
signal alternations. The burst output at pin 6 of the 
i.e. is also used in the RBM chassis for a.c.c. purposes, 
being detected and used to control the gain of the 
chrominance i.f. amplifier. 

Acknowledgement 

The author gratefully acknowledges the help given 
by Rank-Bush-Murphy in the preparation of this 
article. 

TO BE CONTINUED 



14 



mm 




AemalPreamp 



ROGER BUNNEY 



Input coaxial socktt C1 
@ II 




-52! 



* — o- 

9V AF139/6F77I 

0+ undarsM* 



F/ff, 7: Circuit of the aerial preamplifier. 



it components list 



Resistors: 

R1 1k £2 
R2 3-9k a 
R3 10k n 
All £W 1 0% 

Capacitors : 

CI 4*7pF miniature silver mica 
C2 lOOOpFfeedthrough 
C3 2000pF ceramic 
C4 3*9pF silver mica 

Transistor: 

TM AF139or BF272 

Coil: 

L1 2£ turns 0-048in. copper wire (from low- loss 
coaxial cable — inner conductor) wound gin, 
diameter spaced over ^in., tapped at 5 turn. 
(Group A — see text for Band V coil.) 

Miscellaneous: 

Subminiature switch (Japanese d.p.d.t. slide type) ; 
surface- mounting coaxial socket; coaxial plug; 
35mm. metal film can; PP3 battery connector; etc. 



An improved transistor for u.h.f. use, the BF272, a 
low-noise pnp silicon planar type, is now becoming 
available at reasonable prices and we have decided to 
feature this in a simple, basic aerial preamplifier which 
should present little problem in construction. Of 
special interest is that the circuit will work equally 
well with the earlier API 39 transistor which is at 
present available at very small cost: consequently it 
should be possible to build this amplifier for well 
under £1. 



Circuit 

Figure 1 shows the circuit of the amplifier. Signals 
are fed to Trl emitter via CI, Rl providing the 
emitter bias. The base bias components R2, R3 are 
decoupled at r.f. to chassis by C3. The collector cir- 
cuit is tuned by LI, the output being tapped via C4 
into a length (Ift.min.) of coaxial feeder the end of 
which is terminated by a coaxial plug. The feed- 
through capacitor C2 gives extra decoupling for the 
positive supply. 



Construction 

The amplifier is mounted on a small subchassis 
(see Fig. 2) within a metal 35mm. film can. The sub- 
chassis is bolted to the lid by two 4BA bolts which 
also fix the input coaxial socket. The subminiature 
on-off switch together with the leads from the battery 
are also mounted on the lid. Due to the rather soft 
metal used for the hd care should be taken when 
drilling the holes for the various components. The 
battery leads pass through a small hole in the hd, the 
point where the leads pass over the metal edge of the 
lid being protected with a small length of PVC sleev- 
ing to avoid chaffing. 

A metal screen is mounted on the subchassis, the 
purpose of this being to screen the transistor's input 
and output connections in the interests of stability. 
The emitter and base connections are on the input 
side of the metal screen and the collector and shield 
connectioris on the output side, the transistor itself 
being mounted in a hole cut in the screen. The shield 
connection solders directly on to the metal screen. 
The feedthrough capacitor C2 is soldered through a 
hole in the subchassis on the signal input side of the 
metal screen. 

The length of the collector lead-out wire from the 
transistor surface to the coil is 3/16 inch. The output 
lead consists of coaxial cable which should be at least 
lft. long and is fixed to the subchassis by a loop of 
single PVC covered wire. When the wire is twisted 
tight to hold the lead-out coaxial cable against the 
chassis a liberal coating of Bostik no. 1 or some 
similar impact adhesive should be applied : when dry 



Input coaxial / 
socket ,j\ 







On/off 4* 
switch 



Sub-chassis 



Fig . 2; Construction of the preamplifier. 



15 



the lead will be firmly held. The lead-out cable passes 
through a hole drilled in the main body of the film 
can, the hole itself being fitted with a grommet to 
protect the cable. 

In common with all u.h.f. (and v.h.f.) amplifiers 
of this nature it is of the utmost importance to ensure 
that all connections and leads are of the shortest 
lengths possible in order to avoid inferior perform- 
ance. The output coaxial cable must be at least 1ft. 
long in order to damp the output. If it is shorter 
patches of instability may be experienced, especially 
if the input signal is strong. 



Operation 

The coil details given in the components list are for 
group A channels. For group B and C channels one 
turn should be removed and the tapping point re- 
duced to \ turn from the collector. Final peaking of 
the tuning should be done by slightly closing or 



spreading the coil turns. Note the proximity of the 
coil to the edge of the subchassis : when the body of 
the can is screwed into place the change in stray capa- 
citance may affect the tuning, tending to lower the 
frequency. This should be anticipated and the ad- 
justments made accordingly. The bandwidth should 
be found to be sufficient to cover the whole of each 
channel grouping. 

The amplifier draws a current of 2.5mA at 9V. 
The performance of the BF272 is somewhat better 
than that of earlier transistors, the noise figures being 
of special note. The figure (typical) at 800MHz is 
3.5dB, at a gain of 13dB. At 500MHz a gain of 19dB 
is quoted. As mentioned at the start the circuit will 
also work with the AF139 transistor which is more 
readily available than the BF272 and at a somewhat 
lower price. The transistor type BF272 is now listed 
in some advertisements but in case of supply problems 
any ECS outlet can order same or further information 
may be sought from SGS (United Kingdom) Ltd., 
Planar House, Walton Street, Aylesbury, Bucks. ■ 



VARICAP TUNER PANORAMIC MONITOR 

— continued from page 9 

some unusual blips were noticed at the other end of 
the trace — see Fig, 4(a). Zooming in showed them to 
be weak TV signals and the reduced sound /vision 
spacing suggested they came from Europe. A set was 
tuned to these channels and sure enough locked in 
several test cards from Holland and Germany. 

As a field strength meter it is effective but bulky. 
At least all the carriers can be seen at once and this 
helps service managers to reject aerials which give 
erratic responses, tilts etc., rather than letting the rig- 
gers find out the hard, way among the chimney pots. 
The "blip" amplitude is proportional to signal input: 
therefore calibration is linear and with the strip biased 



Local 

Ch TV trio 
'68 



Communication 

ridk) 



3k> i 
21 \ 



DX 
signals 
, i i 



Local TV trio expanded 



8SC1 ITA BBC2 

vision vision vision 





Id 

Fig. 4: Interpretation of the blips displayed, (a) General 
appearance of u.h.f. band swept by the tuner as seen on 
the 'scope. The local duplicated services are on the left. 
On the right can just be seen two DX signals. The blip by 
ch. 21 is some form of communication radio, (b) Zooming 
in on the local stations by using the shift and expansion 
controls shows the sound/vision signal ratio and a form of 
picture content— in this case test card F. (c) Using the 
probe to locate parasitic oscillations. Note the image 
channel which can appear at twice the i.f. {79MHz) 
higher, (d) The probe near the vision detector. Note the 
comb of spikes at 39-5MHz intervals, showing the 
harmonics produced by detect/on. 



Varicap 

tuner _L 



CH3c 



tit appro* coax 



7) 



2 turns 

insulated wire 

round a pencil 

Keep this 

distance shortf 

<-■ 
L- 




Tape covert J 



Fig. 5: Search probe for locating instability. 

to maximum gain a blip rising the full height of the 
'scope trace would be due to a signal of around 300/*V. 
This is an ideal range for weak signals and can be 
extended x 10 to become 0-3mV by fitting a Belling- 
Lee L729/18 — 18dB attenuator at the aerial socket. 

Tracing Parasitic Oscillations 

Another useful application is for tracing parasitic 
oscillations in sets which display beat patterns on 
random channels. Modern i.f. transistors have such 
an improved frequency response that it is not un- 
common to find one singing away to itself quite 
merrily at some u.h.f. frequency just because the i.f. 
leadouts look to the transistor just like a u.h.f. lecher 
bar. 

The method to use here is to fit a search probe to 
the monitor input. This probe consists of a few feet 
of aerial coaxial cable with a plug at one end and a 
two-turn loop of stiff wire at the other (see Fig. 5). 
This probe will home on to your source of oscillations 
with uncanny accuracy. A single burst of uii.f. in- 
stability shows as a very tall thin spike at one point 
on the band with a smaller one at 2 x i.f. (image fre- 
quency) above it — Fig, 4(c). Harmonics of tie de- 
tector produce spikes every 39.5MHz, seen on the 
'scope as a comb-like trace — Fig. 4(d). 

VHF Varicap Tuners 

As previously mentioned v.h.f. varicap tuners are 
available and these can be used in the same way as 
the u.h.f. set-up described. The band switching is 
done by a I2V control potential applied to the band- 
switching pin. This means that if you run your 'scope 
in the double-beam mode by beam switching (if this 
facility is available on it) and can apply the beam 
switching voltage to the band-switch pin on the tuner 
it should be possible to see both Band I and Band III 
at the same time. ■ 



16 



TRRnSISTOR 




CIRCUITS 



S.GEORGE 



A major trend in recent colour and monochrome 
chassis has been the transistorisation of the video/ 
luminance circuitry, in particular the output stage. 
Most c.r.t.s require a video drive in the region of 60V 
for a fully contrasted picture, so clearly the output 
stage must be operated from an h.t. supply rail well 
in excess of this figure in order to provide amplifica- 
tion of the sync pulses as well and to allow for circuit 
losses and tolerances. 

The introduction of transistors such as the BF178 
which can be operated safely from h.t. rails in excess 
of 200V makes possible the use of transistors in the 
video output stages of full-size domestic sets. Several 
current single-standard monochrome chassis use this 
transistor as the video amplifier: in the Pye 169 
chassis for example it is used with a 237V h.t. rail 
while in the Bush-Murphy TV181S/V2016S series it 
is operated with a 228V h.t. rail and in the BRC 1500 
chassis with a 160V, rail. Clearly therefore such a 
transistor video output stage is more than able to 
provide the peak-to-peak voltage swing required, 
especially when it is remembered that the collector 
potential of a transistor can fall to a much lower level 
than the anode potential of a pentode valve. Tran- 
sistorised video circuits in fact usually provide greater 
voltage gain than their valve predecessors, the two- 
stage video circuit comprising a BF197 driver and 
BF178 output stage used in the BRC 1500 chassis for 
example giving an overall voltage gain about twice 
that obtained from a conventional valve video circuit. 

As outlined in the article on h.f. video response in 
the August 1971 issue the load shunt capacitance has 
to be taken into account in calculating the value of the 
video output stage load resistor if the gain is to be 
maintained at the upper video frequencies, since the 
gain falls to 0.7 of the peak (i.e. medium frequency) 
gain when the reactance of this shunt capacitance is 
equal in value to the load resistor. Thus as with video 
pentodes the same considerations of load shunting 
capacitance apply and so load resistors for transistor 
video output stages average about 6-7kSi. 

Bandwidth is the only real restriction in determining 
the load resistor value for a video pentode. With 
transistors power dissipation determines the maxi- 
mum permissible load value though the types evolved 
for video and luminance output stages more than 
satisfy such requirements. There are however two 
conditions which must generally be met. First the 
total base d.c. circuit resistance should not exceed 
about lkH while the emitter resistor value should be 
at least 100 or so ohms. The former condition means 
that the preceding stage must have a low output 
impedance since it will be working into the parallel 
combination of this d.c. resistance plus the transistor's 



input impedance and this combination will probably 
amount to only a few hundred ohms. Vision detector 
load resistors average about 4-5k^ so clearly there 
must be an impedance matching stage between the 
detector and the video output stage or the detector 
efficiency and the loading on the preceding i.f. stage 
will be completely unacceptable (for good detector 
efficiency its load resistor must be of high value com- 
pared with the detector diode's forward resistance 
while heavy loading seriously broadens the selectivity 
of the final i.f. stage). Before turning our attention to 
the impedance matching stage however let us consider 
transistor input impedance in more detail since it is 
vital at video frequencies. 

The input impedance of a common-emitter stage 
with partially decoupled emitter resistor can be 
regarded as being a comparatively low- value resistor 
in parallel with a capacitor whose value is dependent 
on voltage stage gain A. Taking the resistive compo- 
nent first, its value approximates the emitter resistor 
value times the current transfer ratio of the transistor, 
i.e. hiexRe, and if the former is 25 and the latter 
140^ would equal 3-5kfi. The input capacitance is 
rather a different matter involving many factors: Re 
and Me as before, the emitter capacitance Ce, tran- 
sistor feedback capacitance Cre, transition frequency 
fi and voltage stage gain A. The feedback capacitance 
and voltage gain are the most important factors since 
together they account for the major proportion of 
the input capacitance by producing an amplified 
version of Cre across the transistor input in similar 
fashion to that produced by the Miller effect on the 
grid-anode capacitance of a triode (Miller capacitance 
equals Cga times A + l). To see the extent of this 
capacitance, let's consider the BF178 which has a 
feedback capacitance of 2-5pF. If we assume a voltage 
gain of 30, this produces an effective input capacitance 
of 2-5pFx31 or 77-5pF in addition to that of the 
other factors mentioned. These could probably 
amount to a further 20pF so that the total input 
capacitance at this stage gain would be close to lOOpF. 
Clearly as the detector load shunt capacitance must 
be kept to the minimum possible for the same reasons 
as the output stage load shunt capacitance this total 
load capacitance of close to lOOpF cannot be allowed 
to shunt the diode load. Thus for this reason also an 
impedance matching stage is essential. 

For these reasons then the video output transistor 
is usually driven by an emitter-follower stage since 
this has a high input impedance, thus imposing 
negligible loading on the detector circuit, while its low 
output impedance is scarcely affected by the input 
characteristics of the output transistor. An emitter- 
follower provides a voltage gain slightly below unity 
but gives a current gain only slightly below that 
obtained from a common-emitter stage. In some 
recent chassis, such as the Pye 169, a TAA700 inte- 
grated circuit is used for video preamplification, sync 
pulse separation and a.g.c. The video emitter-follower 
is contained within this unit though the emitter load 
resistor is connected externally to reduce the overall 
power dissipation within the i.c. 

Representative Circuit 

Following this general outline let's take a detailed 
look at the operation of a typical modern circuit, that 
used in the BRC 1500 single-standard chassis and 
shown in Fig. 1, Diode W2 demodulates the i.f. 
signal fed to it via C28 from the collector of the 








047 27k Field 

n 1 Blanking 

7 pulses 

L||— VG\— «- 
5kp 220k line 



2400 S 330 
ttffi ftfn 



Heater chain 

'dropper' 



live side of mains 
on/off switch via fuse 



Fig. 1: Transistor video circuits of the BRC 1500 single-standard chassis. 



fourth i.f. amplifier stage, producing both the video 
and 6MHz intercarrier sound signals across its load 
resistor R27 and the peaking coil LI1 (to maintain 
h.f. response peaking coils are just as important in 
detector circuits as in video output stages). The detec- 
tor diode output is negative-going and is superimposed 
on the 5-8V bias potential taken from the junction of 
the potential divider R136, R79 at the end of the 
heater chain which as is usual in current receivers 
uses a rectifier "dropper". C30 and C32 earth the 
bottom end of Lll and decouple this bias. The com- 
bined voltage is then applied as forward bias to the 
base of the npn emitter-follower video driver stage 
Tr8, becoming less positive with increase in signal 
strength to proportionately reduce Tr8 emitter 
current. 

As R136 and R79 terminate the heater chain, 
developing 26V (HT6) across them, if either became 
open-circuit this voltage would rise to an excessive 
figure since the heater circuit continuity would only 
be maintained through the transistors fed from this 
rail. Circuit design however prevents receiver use in 
either of these eventualities: if R79 should go open- 
circuit there would be no forward bias to Tr8 and 
therefore no sound or vision while if on the other 
hand R136 should go open-circuit Tr8 base bias would 
be excessive resulting in a grossly over-contrasted 
picture which would not lock. Additionally if the 
BY 126 heater rectifier should go short-circuit there 
would be no HT6 supply and again no sound or 
vision. 

The video load of Tr8 comprises R33, R34 and R35 
in series, reduction in Tr8 emitter current resulting of 
course in a fall in the potential developed across these 
resistors. The drive for the a.g.c. circuit is tapped 
from R34, the preset contrast control. The a.g.c. cir- 
cuit is of the now usual sync -tip type, R34 thus setting 



the amplitude of the pulses fed to the a.g.c. circuit 
and consequently the a.g.c. bias developed and applied 
to the controlled stages in the i.f. strip. 

The total emitter output is applied via R36, the 
contrast control R37 and C37 as drive to the video 
output stage Tr9, an acceptor trap LI 3, C35 removing 
the sound content from the signal. It is interesting to 
note the difference in the value of the base feed 
capacitor C37 to Tr9 (64/* F) compared to that (C40, 
047 /aF) feeding the same but amplified signal to the 
c.r.t. cathode. This wide disparity is due to the widely 
differing circuit impedances at the two points and the 
necessity to maintain the I.f. response with the low 
input impedance of Tr9 (see "Video L.F. Response" 
in the February 1971 issue). The contrast control is 
effectively the top section of a signal potential divider 
of which the lower section comprises the input im- 
pedance of Tr9 in shunt with R38 and R39 (the h.t. 
end of R38 being earthed signalwise by C38). Thus 
reducing the resistance value of R37 increases the 
proportion of Tr8 output used to drive Tr9. 

The video load of Tr9 comprises R40 and R41 in 
series a.c. coupled to the c.r.t. cathode by C40. R110 
is connected in series with the cathode feed to prevent 
tube flashovers reaching Tr9 collector and causing 
possible damaging surges. R108 varies the c.r.t. 
cathode d.c. potential to give brilliance control. Field 
and line flyback blanking pulses are applied to the 
c.r.t. grid. 

C39 and R42 provide partial emitter decoupling in 
the video output stage, progressively removing the 
negative feedback at the higher frequences (their com- 
bined low impedance then shunting R43) to maintain 
the h.f. response. The 6MHz intercarrier sound signal 
is developed across LI 2, C34 in the collector circuit 
of the driver transistor Tr8 and fed via the 82pF capa- 
citor to the 6MHz i.f. amplifier stage. ■ 



18 



PULSE SCALER SIGNAL GENERATOR 



PART 2 

The output from pin 6 of each uni vibrator i.e. is fed 
to the input pin 3 of the next univibrator (see Fig. 1 
last month). Response at pin 3 is produced on the 
I to transition. Pin 6 rests at and goes to a 1 
during the pulse, so that each univibrator triggers at 
the end of the output pulse from the previous one. 
The sum of the pulse times of IC5 and IC6 is the space 
time between the output pulses of IC4. It is necessary 
to use two space time stages IC5 and IC6 instead of a 
single one because dead-time considerations would 
otherwise preclude space times much greater than the 
selected pulse time. The type MC851P integrated 
univibrator used for IC4 to IC6 possesses a dead 
time which is rather ill-defined on open -circuit and 
amounts to some 40% of the pulse time given by the 
capacitor connected between its pins 10 and 11. Thus 
if IC6 were omitted and IC5 coupled back to the input 
of IC4, IC4 would try to retrigger IC5 before the end 
of its dead time if the space time selected with S3A 
was longer than about 2-5 times the pulse time selected 
with S2. IC5 canqot respond so soon so that oscil- 
lation would cease. 

Starting the Univibrators 

This also underlines the fact that this circuit is not 
self -starting : switching the power supply on, or off 
and on again, will not start the closed ring with SI in 
the "self -excited" setting because these actions do not 
produce the essential 1 to transition at any one of 
the input pins 3 necessary to start oscillation. How- 
ever there is always a logical 1 present at Tr3 emitter 
and thus at contact 1 of SI provided no input signal 
is being fed to PI and the trigger level control VR1 is 
kept turned down. Furthermore all pin 6s of the 
univibrators rest at logical potential. Thus switching 
SI from position 1 to self-excited gives a 1 to tran- 
sition at pin 3 of IC4 and oscillation then commences. 
It will generally stop if the setting of S2 or S3 is subse- 
quently changed so that it is necessary to select the 
desired pulse and space times before switching to self- 
excited or to switch briefly to 1 and then back to self- 
excited if oscillation ceases. 

We must of course ensure that oscillation does not 
cease arbitrarily and this requires sharpening the dead 
times of the univibrators. For this purpose direct 
feedback is taken from output pin 1 to input pin 4. 
Inputs 3 and 4 are equivalent: thus the logical 
placed at pin 4 for the duration of its own pulse 
disables pin 3. Spurious signals arriving at pin 3 — the 
chief cause of occasional erratic prolongation of the 
dead time — -are thus in effect gated out. The capacitors 
between pins 2 and 5 increase the trigger coupling 
time-constant for inputs 3 and 4 to the maximum 
values tolerable in relation to the smallest pulse and 
space times provided so that wanted trigger transitions 
can get through more reliably even in the face of 
occasional partial dead-time barriers. By using these 
artifices oscillation of the ring is made extremely 
secure and will not cease artibrarily even over many 
hours of continuous operation. 



MARTIN L.MICHAEUS MA. 



The two-stage space time generator IC5 and IC6 
permits any space time greater than the pulse time of 
IC4 to be obtained without upper limit. Readers 
requiring other times or longer times may modify the 
values of the capacitors on S3 A and S3B in linear 
proportion. Electrolytics of unlimited size may be 
used, but observe correct polarity. If a continuous 
interpolation is desired between successive capacitor 
values, break the external connections between pins 
9 and 14 of IC5 and 1C6 and connect a 10kH linear 
potentiometer wired as a variable resistor between 
these pins. A tandem potentiometer is desirable for 
ganging the two control points involved. 

The integrated circuits as they stand show a slight 
temperature drift of the pulse times (maximum 5%) 
after switching on. This is due to the temperature 
coefficient of the integrated timing resistor behind 
pin 9. For maximum frequency stability leave pin 9 
disconnected and wire an 8-2kfi fixed resistor in series 
with the lOkil potentiometer between pins 10 and 14 
if interpolation control is desired. 

Pulse: Space Time Ratio (Duty Cycle) 

By virtue of the two-stage space time generation 
with IC5 and IC6 there is no upper limit imposed on 
the space time relative to the pulse time. Irrespective 
of how short the pulse time of IC4, IC5 prevents retrig- 
gering of IC6 earlier than a time interval after the 
end of the previous pulse from IC6 at least equal to 
the duration of that pulse. 

But the space time may not be made shorter than 
about 40 % of the pulse time of IC4 because otherwise 
IC6 would try to trigger IC4 again before the end of 
the la Iter's dead time. Oscillation would then cease. 
To overcome this restriction a four-stage pulse ring 
would be necessary with a two-stage pulse time 
generator. A summing gate would also be required 
to produce a single output pulse of duration equal to 
the pulse times of both pulse time stages without a 
gap in the centre. The considerable additional circuit 
complexity necessary for performing these functions 
was not considered to be worthwhile in view of the 
fact that pulse waveforms with such high duty cycles 
are seldom required. 

If the d.c. potentials are unimportant, i.e. if external 
capacitive coupling is used, a high duty cycle wave- 
form of one polarity is identical to a corresponding 
low duty cycle waveform of the opposite polarity : the 
scaler provides such complimentary output waveforms 
and even if the absolute d.c. levels are important — 
this would be the only real justification for insisting 
on a waveform with a duty cycle exceeding 50% — they 
are easily restored by using a d.c. restorer diode with 
the external coupling capacitor. 

Every attempt has been made in designing this 
instrument to preserve the attractive simplicity possible 
with integrated circuits. The circuit is nevertheless 
considered to be virtually universal with respect to 
duty cycle ranges. The benefits obtainable using time 
interpolating potentiometers were not considered 



important enough for inclusion in the prototype, 
involving as they do an additional manual control. 



The Trigger Amplifier 

The decade counters used as IC1 to IC3 are guaran- 
teed for counting up to 20 MHz, with a typical per- 
formance limit of 30MHz. We therefore decided at 
the outset to design an input amplifier capable of 
driving the input pin 1 of the first integrated decade 
counter from sinusoidal or arbitrary waveform input 
signal frequencies up to 20MHz and with sufficient 
gain to give stable operation with the low input vol- 
tages obtained from very loosely coupled signal probe 
loops consisting of a single turn or a few turns of wire. 
Before commencing work on this project it was feared 
that rather complicated tuned input amplifiers would 
be necessary and that variable capacitors would have 
to be adjusted at least approximately to the band in 
which the frequency to be counted lay if this was well 
above 1 MHz. These fears proved to be quite un- 
founded. A very simple aperiodic input amplifier will 
do the trick very well and requires no tuning controls. 

Nevertheless roughly 90% of the time devoted to 
designing this circuit was spent in devising the best 
arrangement for Trl to Tr3 and the few components 
associated with these stages. Basically an input ampli- 
fier is not required at all because IC1 will operate on 
sinewave signals fed direct to its input pin 1 provided 
the frequency is high enough to ensure the minimum 
required trigger slope. But such a direct connection 
is undesirable for several reasons. Control is not 
stable, and the desired trigger sensitivity of about 
lOmV r.m.s. is not realisable over a wide range of 
input signal without a suitable amplifier. Even slightly 
excessive signal amplitudes fed direct to pin 1 of IC1 
can destroy this integrated circuit, especially if going 
negative to chassis. 

Nominally the decade counter MC838P is toggled 
(made to respond) at pin 1 by applying the standard 
1 to logic transition. This would imply that a rapid 
change is required from a potential greater than 2V 
to one less than IV, in keeping with the definition of 
the logic levels in this family. Experiments revealed 
however that the MC838P does not require this large 
logic swing for toggling. It will not respond at all 
to a rather slow drift down from the 1 level to the 
level but on the other hand it does not require the 
extremely fast dynamic transition needed to fire an 
MC851P uni vibrator i.e. at its pins 3 and 4 because the 
decade counter does not employ input differentiation. 
The actual response point lies somewhere between 
+ 1V and +2V with respect to chassis at pin 1 and it 
suffices to provide a reasonably fast transition from 
about 150mV above this point to 150mV below it to 
give a count. This represents a peak-peak logic swing 




-M- 

Old 
BYY33 



D11 
BYY33 

-M- 



R18 
SB 2W 
f-VW 



100 iw 

■vw 



^ — r 

■tan i 

AZDS-1 T" 



C53 

100 



-*-SVU) 



R19 
220 IW, 



1 T 

90)3 — 

1 ZD5 'T 



-fcSV(b) 



C51 
100 






R20 
*70 

iCSI iCS2 
'2200 T 100C 



t icss 

Z05-lyl00 



■5V(e) 



Fig. 3: Power supply circuit. 



19 

of only about 300mV. Optimum sensitivity is obtained 
if the signal excursions at pin 1 of IC1 are confined to 
this small range around the actual response point. The 
necessary large d.c. potential (about I-5V) correspond- 
ing to the position of the response point (which is 
subject to manufacturing tolerance) must be added 
to the small signal waveform in a stable and smoothly 
controllable manner. Above all this d.c. backing 
potential must be extremely efficiently smoothed, since 
very small hum levels would seriously impair the 
utilisable sensitivity. 



Gain and Trigger Level Control 

The adjustable d.c. backing potential is provided via 
the trigger level control VR1. The supply voltage for 
the entire trigger amplifier is stabilised by a zener diode 
and the sample used for deriving the backing voltage 
is further stabilised by diodes Dl to D4 to remove the 
last traces of hum. CI, R4 and D5 form a d.c. restorer 
circuit capable of operating up to 20MHz. Any 
common r.f. diode is suitable for D5. The input wave- 
form is d.c. restored positively with respect to the 
backing potential at VR1 slider so that the negative 
signal peaks lie at VR1 slider potential because D5 
briefly conducts during each such negative peak to 
return to CI the charge which has leaked away 
through R2 and R4 during the rest of the previous 
signal waveform cycle. It is thus possible with VR1 
to lift very small signal excursions to the correct mean 
potential for narrow toggling across the actual 
response point at pin 1 of IC1, VR1 is a d.c. control 
which does not handle the actual signal frequency 
voltages, thus obviating all the problems associated 
with stray capacitances with r.f. gain controls. 

Gain Factor 

Experiments with small inductive loop signal probes 
connected via an r.f. detector probe to an electronic 
voltmeter showed that typical induced voltages 
between lOmV and IV r.m.s. in the range from 100kHz 
to 20MHz using this kind of loose coupling minimised 
the oscillator loading (depending on the amplitude 
and Q factor of the sensed oscillator circuit). The 
minimum required logic swing of a properly backed 
signal at pin 1 of 1C1 is about lOOmV r.m.s. Thus a 
gain factor of 10 is required for the trigger amplifier 
to give the required maximum input sensitivity of 
lOmV r.m.s. This gain factor is obtained as follows: 
the ratio of R8 to R9 is about 5 and the ratio of RIO 
to R9 somewhat greater so that the positive feedback 
from Tr2 collector via Tr3 emitter to Tr2 emitter is 
insufficient to sustain oscillation or to produce a 
threshold trip. But this positive feedback increases the 
effective gain of the combination to about 10. 

To cater for large input signal amplitudes as well as 
small ones Trl and Tr2 rest completely cut off when 
VR1 is set to zero. Tr3 rests saturated so that a poten- 
tial close to the collector supply voltage is applied to 
pin 1 of ICL This is a logical 1. The potential at 
pin 1 of IC1 cannot rise above +5V and it cannot go 
negative to chassis. Thus destruction of IC1 is 
precluded. 

Large Signal Voltages 

The base of Trl must be driven positive to chassis 
by at least the silicon thresholds of Trl and Tr2 plus 



20 

the standing potential at Tr2 emitter — due to the cur- 
rent flowing through Tr3 — before any change at all is 
felt at pin I of ICI. This minimum positive excursion 
required to open the amplifier is about 1-6V. In 
operation part of this excursion is provided by the 
peak-peak swing of the positively restored signal vol- 
tage appearing across R4 and the rest is made up by 
advancing VR1 the necessary amount. The range of 
VR1 is sufficient to open the amplifier in the complete 
absence of a signal. This is necessary because the 
entire backing voltage must be provided with VR1 
when triggering on very small input signal amplitudes 
(maximum usable sensitivity setting). The larger the 
input signal the lower down on its track will be the 
proper setting for VR1. 

The small tabulation on the circuit diagram (Fig. 1) 
shows the corresponding voltages measured at pin I 
of 1C1 for respective voltages produced in the absence 
of any input signal at the junction of R2 and R3 by 
adjusting VR1. These pairs of voltages should be 
checked to test the proper performance of the ampli- 
fier. Evidently about +2-0V must be present at Trl 
base to drive the potential at pin 1 of ICI to the critical 
response point of about + 1-5V. Thus the correct set- 
ting of VR1 is at the chassis end of the track with input 
amplitudes of about 2V peak-peak or some 700mV 
r.m.s. For still greater input amplitudes it is unneces- 
sary to use the trigger level control at all and it may 
be left with the slider at the chassis end. Input voltages 
appreciably greater than about 700mV r.m,s. 
nominally overload the amplifier. R7 has been added 
to make the circuit capable of handling inputs of up 
to several volts without unstable triggering. These 
bottom Tr2 so that R7 and R9 then function as a 
voltage divider with Tr2 merely behaving as a series 
diode. Somewhat greater input voltages bottom Trl 
too, leading to much heavier attenuation via R3, R7 
and R9 as a voltage divider. This arrangement makes 
it unnecessary to use any form of manual gain control. 
Really excessive input signals are easily avoided by 
using an external attenuator or by avoiding placing 
an inductive loop probe too close to the oscillator 
being sensed. 



Frequency Range 

The trigger amplifier initially tried was a more con- 
ventional version with larger value resistors and a 
speed-up capacitor across RIO to steepen the threshold 
response flank obtained, with R8 large enough to 
produce sufficient positive feedback for instability. 
This is the classical Schmitt trigger arrangement used 
to produce sharp logic transitions for operating ICI 
from any arbitrary input waveform which does not 
have such sharp transitions. This circuit, which was 
used for exactly the same functions in the 100kHz 
digital frequency meter, gave no success here. It per- 
formed excellently up to 100kHz— as in the digital 
frequency meter — and with considerable coaxing and 
poor smoothness of the trigger level control would 
work up to about 2MHz. The trouble was found to 
be due to the stray capacitances around the transistors. 
The methods of inductive and /or capacitive frequency 
compensation used in wideband oscilloscope ampli- 
fiers produced responses up to nearly 10MHz, but in a 
rather erratic manner and above all with such poor 
input sensitivity that their value was considered very 
dubious. 

In the course of these experiments it emerged that 



any form of threshold trip response seemed unde- 
sirable because its inevitable associated hysteresis is 
greater than the smallest logic swing with which ICI 
will operate, so that a tripping amplifier seriously 
impairs sensitivity and makes trigger level adjustment 
tricky and subject to severe backlash. Thus the only 
simple way to obtain the desired bandwidth of 20MHz 
is to reduce the resistor values drastically so that the 
inevitable stray capacitances are without significance. 
It was decided at the same time to reduce R8 and 
increase the ratio of RIO to R9 so that a trip is just 
no longer possible. This proved to be successful in 
every respect and is the final form of the circuit as 
published. 

Experiments with tuned amplifiers were made at an 
early stage of the design work but were soon aban- 
doned because they brought no clear advantage in 
terms of sensitivity or stability. Tuned circuits func- 
tioned — indeed up to 20MHz — but the tuning was 
rather critical and the manual operating procedure so 
tricky that a clearly formulated operating procedure 
would have been impossible. With the adopted simple 
aperiodic amplifier however the operating procedure 
is extremely simple. 



Operating Procedure 

The operating procedure in the self-excited mode 
should be clear from the circuit description. Similarly 
the scaling mode when used for producing lower pulse 
frequencies than the lowest available directly from 
standard pulse generators, or for dead-time measure- 
ments in conjunction with flutter scaling, has also been 
described adequately. Thus the present instructions 
are confined to the scale mode used for r.f. measure- 
ments in conjunction with the digital frequency meter. 

It is convenient to class frequencies up to 100kHz 
as audio and supersonic which the digital frequency 
meter will handle directly, and frequencies above 
100kHz as radio frequencies which require the use of 
the 20MHz pulse scaler. The preferred method of 
signal injection into the scaler is via a loosely-coupled 
inductive loop connected either directly to PI and P2 
or connected to the end of a piece of coaxial cable 
whose other end is connected to PI. A special signal 
probe is not necessary because the length of coaxial 
cable, the number of turns of the loop and the 
diameter of the loop are in no way critical. A con- 
ventional grid-dip meter covering the range 100kHz- 
20MHz is extremely useful in conjunction with the 
20MHz pulse scaler for numerous types of measure- 
ments. 

If for example it is desired to measure the fre- 
quency to which a radio receiver is tuned in the long, 
medium or shortwave bands, first determine the 
approximate frequency from the receiver tuning scale 
and then tune the grid -dip meter — coupled loosely to 
the aerial socket — to approximately the correct fre- 
quency (not the image frequency) according to its own 
scale. The grid-dip meter can then be tuned critically 
for zero beat frequency with the received station heard 
in the loudspeaker. The beat frequency should be 
reduced to below 1kHz corresponding to the sub- 
sequent resolution of the digital frequency reading for 
shortwave frequencies. Without disturbing the setting 
of the grid-dip meter, its coils can then be approached 
by a small single-turn coupling loop plugged directly 
into Pi and P2 of the scaler and a digital frequency 
reading taken as described below. This procedure will 



; 




21 



rapidly log the frequency of a shortwave station to 
within + 1kHz which is fully adequate to identify it 
positively but quite impossible with reference to the 
tuning scale of any ordinary domestic receiver alone. 

With a little practice the frequencies of v.h.f. radio 
and television transmitters can be determined in a 
similar manner, using harmonics of the grid-dip meter 
frequency to beat against the carriers. The only 
additional requirement in this case is to be able to 
identify the particular harmonic, which implies that 
the frequency to be measured must be known approxi- 
mately to within about ± 10MHz which is usually the 
case because this tolerance is within the resolution of 
the receiver tuning scale. Television Band III fre- 
quencies will for example require up to about the 
tenth harmonic of the grid-dip meter operating on its 
highest range, so that the ultimate resolution of the 
digital frequency reading can theoretically be as high 
as 10kHz. 

Digital readings of the resonant frequencies of 
passive circuits can be obtained analogously. This is 
an extremely useful facility for dimensioning peaking 
coils in video amplifiers and filters with much greater 
precision than is possible with reference to the grid- 
dip meter scale alone. To obtain a reading, find the 
dip with the grid -dip meter in the normal manner, 
finally coupling as loosely as possible to get the best 
fine tuning of the dip, and then measure the frequency 
of the grid-dip meter digitally. 

Signals may be fed via cable directly from the 
output of a standard r.f . signal generator to the input 
socket PI. The operating procedure is the same 
whether the signal is injected by cable or picked up 
by a small inductive loop. 

Always commence with the trigger level control set 
to zero (slider at the chassis end of the track) and select 
a division ratio with SI such that the output frequency 
will not exceed 100kHz which is the nominal maxi- 
mum input frequency for the digital frequency meter. 
Either P3 or P5 should be connected to the pulse input 
of the digital frequency meter via a short piece of 
coaxial cable and VR3 or VR2 set to give an output 
amplitude of about 5V. This is not critical. S2 must 
be set to 10 or 20 microseconds. The setting of S3 is 
immaterial because the pulse ring is inoperative in this 
mode. 

Slowly advance the trigger level control until stable 
response is obtained. If the input signal level is large 
it will not be necessary to advance VR1 at all. If the 
input signal is small however VR1 requires precise 
adjustment which becomes the more critical the 
smaller the signal voltage is. For small signal voltages 
there will always exist a small range of settings of 
VR1 below and above which response ceases. Below 
this response range the backing voltage is still too 
small so that the signal excursions do not reach the 
toggle swing of IC1 whilst above the response range 
the backing voltage is already too large so that the 
small signal excursions have been pushed entirely 
beyond the toggle range. The range of settings of 
VR1 giving a response become progressively narrower 
as the signal amplitude is reduced so that ultimately, 
with only about lOmV r.m.s. input signal, response is 
obtained only at a spot setting near the top end of the 
track of VR1. 

The correct procedure for ensuring that the 
response is secure so that all cycles of the input signal 
are counted without any being missed is as follows. 
Switch the digital frequency meter to the analogue 



mode giving a direct linear frequency reading on the 
thousands meter. Select a range on the frequency 
meter giving an on-scale reading with the expected 
(approximately known) frequency. Now adjust the 
trigger level control whilst observing the thousands 
meter giving the analogue frequency reading. With 
VR1 set far from the proper position there will be no 
reading at all. As the correct setting of VR1 is 
approached a reading will appear but will be far too 
small and fluctuating erratically because only some of 
the signal cycles are operating IC1 since their excur- 
sions are still askew with respect to the toggle swing 
of ICI. Further judicious advance of VR1 will now 
bring a steady reading which persists over a certain 
range of still further advance of VR1 beyond which it 
again becomes erratic and then vanishes. The correct 
setting for VR1 is at the centre of the range giving a 
steady analogue frequency reading. The digital fre- 
quency meter can then be switched to the digital mode 
to take the final reading in the normal manner. 



Construction and Testing 

There are no critical points in the construction of 
the 20MHz pulse scaler. As with the frequency meter 
layout diagrams are available on request. These 
should be observed and will take care of all the prob- 
lems involved on account of the very high frequencies 
involved, calling for short wiring at critical points, 

Do not use transistors other than those specified; 
or if you do be prepared to modify resistor values 
slightly if necessary. Trl, Tr4 and Tr5 must be high- 
beta types (beta at least 200 but preferably not greater 
than 400 since otherwise the frequency response may 
suffer). Tr2 and Tr3 must be low-beta types (beta 
about 30, not exceeding 70). Any silicon or germanium 
r.f. signal diode is suitable for D5. D1-D4 must be 
silicon diodes but the actual type is unimportant. D8, 
D9 may be any silicon or germanium r.f. diodes. ICI 
to IC6 are standard packages in the Motorola DTL 
range and are readily available. Only packages listed 
as direct substitutes for the specified Motorola types 
may be used as alternatives without redesign of the 
circuit. Modifications permissible to give other pulse 
and space times and to provide continuous interpola- 
tion control if desired have previously been discussed. 

The instrument requires no presetting and is ready 
for operation as soon as construction has been com- 
pleted. If correct performance is not obtained check 
the voltage readings shown on the circuit diagram. 
The voltages given are with respect to chassis and 
should be measured with a high-impedance voltmeter. 
They are valid with no input signal, VR1 at zero and 
SI not set to self -excited. The voltage at SI slider is 
either +160mV or +4V depending on whether the 
output of the scaler chain is in the logical or 1 stage. 
This can be changed by applying a signal to PI and 
adjusting the trigger level control accordingly. 

The trigger amplifier can be checked by advancing 
VR1 progressively to produce the tabulated voltages at 
A and checking the corresponding voltages at B. Con- 
trol of the voltage B by the voltage A must be without 
any backlash or threshold trip behaviour. If this 
condition is not satisfied one of the resistors R8, R9 or 
R10 is too far out of tolerance so that these resistors 
must be checked with a good ohrnmeter and the 
offending one replaced. It is advisable to check these 
resistors before soldering them on to the printed circuit 
board. 



22 




SERVICING 

{television 
receivers 

L. LAWRY-JOHNS 

PLESSEY DUAL-STANDARD CHASSIS 






The original Plessey dual-standard chassis was pro- 
duced in the 1963-64 period and was used in a very 
large number of receivers. Many of these sets are 
now on the second-hand market under various brand 
names and suitably serviced can provide several 
more years of good viewing. We list the following 
models but do not claim the list to be complete by any 
means: Defiant Models 9A50, 9A51, 9A52, 9A56, 
3A54, 3A60; Cossor Models CT1 964/77 and 78; 
Challenge Model C501; Peto Scott Models TV960 
and TV960/90; RGD Models 624 and 625; Regentone 
Models 195 and 196. 

The differences which occur will be found in the 
type of tuners fitted (push-button or rotary v.h.f.) 
and in the vision i.f. strip which may use an EF184 
or an EF80 (early versions) in position V2. The 
position of the choke L2 may be at the top centre of 
the chassis or on the right side above the line output 
transformer. The mains dropper may be of the multi- 
tag type (which fails all too often) or the three-tag 
type (which doesn't). 

There is a great deal of difference between being 
asked to carry out a quick repair on one of these 
sets and to renovate one for continuing reliable 
operation. In the first instance one traces the offend- 
ing fault and rectifies it. In the second one would 
check up on all likely trouble spots and replace some 
components before they have a chance to fail. This is 
of course more expensive and time consuming but 
it does pay handsome dividends in the long run. 



Faulty Dropper 

Most of the older models used an unreliable drop- 
per on the right-hand side any section of which could 
fail at any time. If one can obtain a more reliable 
dropper of the same total value it is a matter of 
minutes to unclip the old one and fit the new with 
no soldering necessary. A dropper which is adorned 
with bits and pieces of shunt resistors is not only 
unsightly but electrically unreliable (even this how- 
ever is preferable to shorting out the faulty section 
and thereby ruining the set by over- running it). 



Blown Fuses 

There are two fuses in insulated carriers on the 
left side. The one nearer the rear is the mains fuse 
1-5A. The second one is the h.t. fuse, 500mA. The 
latter is the one which will mostly be found blown. 
It will fail when there is a short anywhere in the h.t. 
line except in the rectifier and reservoir capacitor. We 
exclude the smoothing choke and brilliance circuit 



from this as these rarely give trouble. Assuming that 
the symptoms are that the valves are lighting up but 
nothing else is happening, this fuse should be checked. 

If it has failed it is reasonable to assume that 
somewhat more than 500mA has tried to pass through 
it. If there is no sign of h.t. at either end of the fuse 
holder and the fuse has not failed, one of the sec- 
tions of the mains dropper will almost certainly be 
found to be open-circuit. Proceeding on the assump- 
tion that the fuse has failed however a visual check 
should be made for signs of recent overheating. It is 
a rule with this chassis that the upper panel should be 
swung out to check the condition of the resistive 
element 124 in the video stage V3. This consists of 
two resistors* one lOkO the other 8-2kn. Both tend to 
change value thus passing excessive current. This 
damages 122 and 123 whose mode of protest is also 
to change value downward until a virtual short is 
presented across the h.t. line. 

Now this state of affairs should never arise if the 
viewer has been at all critical in his (or her) viewing 
since the quality of the picture' would have deterior- 
ated to an extent which should have called attention 
to the developing fault long before the virtual short 
condition occurs. But it is in the nature of things 
that people do tolerate the most atrocious viewing 
and sound conditions and tend to wait for complete 
failure before having something done about it. 

We will have more to say about the symptoms 
caused by changing value in these resistors later but 
we are still concerned for now with h.t. shorts. It is 
worthy of mention that the h.t. tracks on the panel in 
the vicinity of the video stage and the contrast con- 
trol run down very near the edge. This makes them 
not only liable to fracture but also to short to the 
metal clips if the insulation is accidentally removed. 

If there is no sign of trouble in this stage however 
observe the state of the choke L2 if this is mounted 
on the right side above the line output transformer 
housing. This choke tends to sag wearily after a 
period of use and the exposed end tag can touch the 
top of the housing. Usually by the time this state of 
disarray has been reached however the choke has lost 
enough inductance to stop the line output stage 
functioning. This rather surprising fact is worth re- 
membering when one is looking for a line output 
stage fault and is one of the reasons why the choke 
was more rigidly mounted at the top centre in later 
models. 

Assuming however that the choke is maintaining 
its rightful place and that the video resistors are 
healthy looking attention should next be directed to 
the PCL82 sound output stage. This valve can short 
inside, cook up its cathode resistor (and capacitor 






23 




Fig. 1: Rear chassis view. In later versions L2 is mounted at the top centre of the chassis. Loudspeaker position and type 

of v.h.f. tuner used vary from model to model. 



most likely) and cause the fuse to fail. This can also 
apply to one of the EF184 valves if these are used. 
All these items show visual signs of where the fault 
may be located before the aid of a meter is sought 
in order for example to find a shorted capacitor. We 
have found that whilst capacitors do fail in this 
chassis they do not often do so where they would 
constitute an h.t. short. 

Line Timebase Troubles 

The line output transformer itself is one of the 
trouble spots. Usually when faulty it produces a no 
e.h.t. condition and it is reasonable to assume that 
when the valves check out, the boost capacitor (568), 
the line drive and the lOG^F electrolytic (564) are 
all in order the transformer is indeed at fault. When 
replacing be sure to obtain the correct replacement to 
avoid a lot of sorting out of revised connections. One 
of two types may be found: the Original has a black 
overwind and a separate coil (all connections except 
one on the outside); the later one is an encapsulated 
design with no separate coil, a white covered over- 
wind and all connections on the inside. In some 
cases the chassis member of the early models will not 
accept the later transformer without some degree of 
cutting. Stubborn cases of reduced width are often 
due to a faulty transformer and failure of insulation 



often occurs particularly on the separate 625 winding 
which is under the overwind. If the set is used on 405 
only it is possible to disconnect this winding com- 
pletely and at least keep the set going until another 
transformer is obtained. 

In most cases however the transformer is not at 
fault and the usual checks soon reveal the trouble. 
Removing the top cap of the PY800 will often bring 
the line output stage to life thus denoting an alterna- 
tive h.t. path to the transformer, most often a shorted 
boost reservoir capacitor (568, 0-25p,F). Also check 
the WOjjJF electrolytic 564 if removing the PY800 
top cap makes no difference, and the condition of 
the previously mentioned choke L2. 

Whilst the PL36 and the PY800 should always be 
suspect the line oscillator ECH84 rarely gives trouble 
and line hold troubles usually respond to a check on 
the diodes and small components on the detachable 
centre line sync discriminator panel (plug-in). 

Sound Faults 

Usually the only trouble to be expected apart from 
hum on 625 concerns the PCL82 output valve. Check 
this valve and particularly the condition of the 
cathode bias resistor 142 (390Q). Quite often the 
valve is changed but the bias resistor is forgotten 
leading to an early repetition of the valve failure due 



24 




Fig, 2: Circuit of the first P/essey dual-standard chassis, SW1/8 shorts the junction of 122, 1 12 to chassis on 405, With 



to insufficient bias. The electrolytic capacitors in this 
stage can become open-circuit without much attention 
being drawn to them. This is because there is usually 
a good reserve of gain and the fact that the volume 



control has to be advanced more than is normal may 
pass without comment. Check capacitor 106 (0-01jttF) 
if the PCL82 is passing too much current and the 
cathode resistor and the valve itself are OK. 






25 



^ * Convnon HT 




Tso.s £"-U i™ on HiMtoii 

printed tire mi board 

Switch*! shown In 625 position 



Capacitor 214 is 27 pF or 18pF depending on type of tuner fitted, 
the encapsulated line output transformer 468 is 260pF and capacitor 472 is omitted. 



It is not unusual for the 625 sound to deteriorate 
making accurate tuning on u.h.f. difficult. This is 
often due to slight drift in L41-42 and L43-44. Slight 
adjustment with a suitable trimming tool (hexagon 



wand) should restore normal tuning. These cores are 

on the upper left of the panel. Do not disturb the 

lower cores at all as the picture quality is easily lost. 

CONTINUED NEXT MONTH 



26 



BASIC CIRCUITS 

THIS MONTH: AUDIO CIRCUITS 

High-quality sound in a television receiver is unusual 
and some readers may consider it to be unnecessary. 
The sound signal transmitted by the broadcasting 
authorities however is usually up to a very high stan- 
dard and one cannot help but wonder why such high 
standards are maintained when the majority of re- 
ceivers are equipped with mediocre audio amplifiers 
and small loudspeakers. The constructor is in a posi- 
tion to be able to take advantage of the high-quality 
transmissions if he wishes. 



Low-power Circuit 

Two different circuits are described in this month's 
article, the first of which is the conventional three- 
transistor approach shown in Fig. I, The 625 or 405 
sound signal is selected by RLY501 and passes via the 
volume control to the base of Tr50I. The amplified 
signal at the collector of Tr501 is impedance matched 
into the loudspeaker by the complementary output 
pairTr502/Tr503. 

D.C. bias for the circuit is obtained by a resistive 
feedback network (R502, VR502) from the junction 
of R503 and R504, VR502 being set so that the voltage 
at this junction is half the negative rail voltage. Bias 
stability is maintained by virtue of the high open-loop 
gain of Tf501 — if the midpoint bias at the junction of 
R503, R504 tends to drift upwards Tr501 base voltage 
will increase causing a reduction in its collector vol- 
tage so that the initial drift is compensated. The 
quiescent (zero signal) collector current of Tr502 and 
Tr503 is determined by the voltage drop across D501 
which is a bias diode specifically designed for use 
with AC128/AC176 complementary output transistors. 

From die signal viewpoint Tr501 drives the com- 
plementary output pair, Tr502 conducting on the nega- 
tive-going transitions of the drive waveform and Tr503 
on the positive-going transitions. The closed-loop a.c, 
voltage gain of the amplifier is approximately 15; 
thus IV p-p is required at the input to drive the am- 
plifier to full output. Into a 15fi loudspeaker the 




J.W.THOMPSON 



output power is about 1W which is quite sufficient 
for normal domestic use. Into a 30. loudspeaker the 
power output will be somewhat greater but will not 
approach the theoretical maximum level of 5W due 
to impedance mismatching. The maximum output 
power (Fmax) available from a correctly matched 
audio amplifier is given by the following expression : 

/-3 
Pmax 



-P 



■*■ Zl, 



where V is the supply voltage and Zl is the loud- 
speaker impedance. 



IStrip* 



AC128 
AC176 



CS01 
To pin )S p n - 



To C«S» 




Fig, 1: Low-power audio amplifier. 



Table 1 : Brief performance specifications. 



Amplifier 


Maximum 

output power 

(UK r.m.s. watts) 


input voltage for 

maximum output 

(p-p volts) 


Total harmonic 

distortion at 80% 

of maximum 

output 

(tkHz sinewave) 


Frequency response 


3-transistor with 
15H LS and 15V 
supply 


1W 


1V 


2% 


20 Hz-15kHz±2dB 


10-transistor with 
3Q LSand 15V 
supply 


5W 


1V 


< 0-1 % 


15Hz-50kHz±1-5dB 
(see also Fig. 3) 


1 0-transistor with 
3 £2 LSand 30V 
supply 


20W 


2V 


<G-1% 


As above 













27 



STEPHENS 



ELECTRONICS, 
24 PARTON ROAD, 
AYLESBURY, BUCKS. 



SEND S.A.E, FOR LISTS 

GUARANTEE 

Satisfaction or money 

refunded. 



GUARANTEED VALVES BY THE LEADING MANUFACTURERS BY RETURN SERVICE 
1 YEAR'S GUARANTEE ON OWN BRAND, 3 MONTHS' ON OTHERS 



AZ31 

AZ50 

CBL1 

CBL31 

CYfll 

DAF91 

DAF96 

DF91 

DF98 

GK91 

DK96 

DL92 

DL34 

DL96 

DM70 

DY86 : '7 

DY802 

E55L 

E88CC 

E130L 

E1H0F 



Slip 

hop 

SOp 
85p 

35p 
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67 ip 
67 ip 
37 J p 
37 p 
46? 
32 -p 
40p 
4S*p 
£2 -5 
40p 
£4 50 
95p 



EABC80 52 1 p 
EAF42 60p 



EBC33 
EBC41 
BBC81 
EBC90 
EBF80 
EBF83 
BBFS9 
EB91 

Bcoa 

EC86 

B0S8 

EC90 

EC 92 

EC93 

BOC81 

K«JC82 ; :t 

BOC84/5 

BO088 

EHSCC 



5Sp 

47 (p 

32!p 

47lp 

40p 

40p 

40p 

SUP 

Slip 

SOp 

eop 

SOp 

SB'.p 

47 Ip 
40p 

42jp 

42!p 
SSp 

B2jp 



ECF80/2 47Jp 
i-:CFm; 55i> 



Ken;::. 
BCH4B 
ECHS1 

ECH83 
ECH84 

BCLM 
ECLS2 

ei.:i.»h 

ECLSfi 
ECLL80O 

EF39 
EP8U 
EF83 
EFH5 
EF86 
KF.Si) 
EF91 
F.V-I 
EF93 
EF94 

i-inm 
EFIH3 
EF184 
BSB8F 

K|.'«(IIJ 

BF8&4 

!■.]■■« I J 
BI44 
EL 30 
E1.41 
HUB 
F.LHl 
BL83 
ELK5 
BL86 
EL90 
Ml.SII 

EI.95 

Buae 



67 ip 
88p 
Sip 
40p 

47Sp 
40p 
49p 

67!p 
49p 

£1-50 
52:p 
40p 
SOp 
41p 
68p 
40p 
42Ip 
EOp 
47 Ip 
77Jp 

eeip 

S6p 

3Sp 

£210 

£100 

£1 00 

7Sp 

S2iP 

47jp 

55B 

57lp 

SOp 

41p 

42ip 

42(P 

38!p 

25p 

35p 

£1 15 



BL303 


85p 


EL82I 


55p 


ELLBO 


76p 


EM34 


SOp 


EM 71 


62ip 


EM 80 


40p 


EMS1 


42lp 


EM84 


37»p 


EM87 


55p 


EX91 


32Jp 


KYfll 


40p 


EY80 


45p 


EY8 1 


40p 


EY83 


55p 


EY8S 


40p 


EY87 


42tP 


EYSS 


48lp 


EZ3J 


271p 


EZ40 


45p 


EZ41 


45p 


EZ80 


27 ip 


EZH1 


271p 


EZ90 


25p 


G910C 


£5 00 


GYoOl 


SOp 


GZ3U 


37 Ip 


GZ31 


30p 


GZ32 


47+p 


GZS.'i 


SOp 


0284 


5Sp 


HK90 


32jp 


HL92 


35p 


HL94 


40p 


KT66 


£137t 


KT68 


£1-66 


N78 


£1-05 


PABCai 


40p 


PC86;8 


Sip 


PC 93 


3flp 


PC 97 


41p 


PCCS4 


48p 



PCC8S 

PCC88 

FCCSH 

PCC189 

PCF80 

PCF82 

PCF84 

PCF86 

PCF3O0 : 

PCFSOI 

PCFS02 

PCF805 

FCF806 

FCF808 

PCH209 

PCLS2 

PCL83 

PCL84 

PCLS5 

PCL86 



v5.? 
70t> 

Dip 

Sip 
Sip 

47 ; P 

Sip 
Sip 

flip 

Sip 
55 p 
SI; 

ST.p 
70p 
Sip 
Sip 
Sip 

iO 
Sip 



PD5O0 £1 521 
PFL200 74p 
PL3G 



PL38 

FL81 

PL81A 

PL82 

PLB3 

FL84 

PL3Q0 

PL504 

P 1.5 05 

PLJ08 

PI.-50S 

^ , L^:l^ 

PI.W5 

FY33 

PY80 

PY81 

PYVjO 

PYnOl 



64p 

SOp 

Sip 

62 Ip 

36p 

Sip 

41p 

S2=-p 

SSp 

£1-45 

£100 

£1-54 

86p 

86p 

6f,'p 

3StP 

41p 

■ilr 

41p 

35p 



FY 83 


SOp 


PY8S 


41p 


I'YOOO 


£1 00 


pz;w 


SOp 


CJQUO2-S£2 10 


QQUO3-10 




£1 25 


QV03*iS 


; 5p 


R19 


SSp 


1120 


75p 


3U2150J 


76p 


TT21 


*2-40 


TT22 


££50 


U18 20 


67fp 


L"20 


67 p 


U25 


75p 


UM 


75p 


L"31 


45p 


E37 


£1-50 


irari 


aop 


U52 


3 Op 


V7S 


2Sp 


U78 


25p 


L'191 


75p 


l"2ill 


3Sp 


U281 


40p 


U282 


40p 


rsoi 


p,">P 


U40S 


sop 


U404 


37jp 


U801 


£1-00 


UABC8C 


S2]p 


UBFH9 


40p 


UBC41 


49p 


(70089 


46p 


VCH42 


69p 


t:chsi 


54p 


CCI.82 


Sip 


CCL83 


Sip 


UF41 2 


55p 


UFBO 5 


37|P 
41p 


CF89 



UL41 

ULH4 

TMMH 4 

LV41 

VY83 

U25 

I.-2S 

L"191 

U19H 

I'SUl 

W72B 

Z759 

OA2 

OA3 

OB2 

(III:, 

OC:t 
OD3 
3Q4 
334 
3V4 
SB40Y 

m*a 

5V40B 
3V4G 

SY3r:T 

na 

5241 IT 

■•> :inl,2 

SAB4 

fiAF4A 

BA07 

OAMO 

'iAI8 

OAKS 

OAKfi 

0AL3 

BAL5 

0AM5 

liAM'! 

<>M<- 

SAQO 



57*p 
SSp 
45p 
40p 
34p 
7Sp 
7Sp 
72iP 
41p 
SSp 
SSp 
£122' 
32ip 
45p 
32JP 
SOp 
35p 
32!p 
40p 
3Sp 
40p 
SSp 
SOp 
37ip 
40p 
30p 
4Sp 
40p 
75p 
321P 
47!p 
37Jp 
SOp 
2Sp 
SOp 
S7jp 
42)p 
16p 
SSp 
22}p 
32}p 
SOP 



fiAR.i 


32. p 


CAHti 


22 P 


(£89 


SSp 


HAS7C 


SOp 


OAT)) 


45p 


BAUfi 


29p 


6AUfi 


30p 


BBA6 


474p 


6BE6 


SOp 


OBKi] 


42(p 


■:'•:.]!, 


421p 


0BK7A 


SOp 


liBI," 


35p 


BBN5 


421 p 


BBSS 


40p 


BBQS 


25p 


BBB7 


76p 


BBRS 


95p 


BBWti 


82ip 


SEW! 


89p 


BBXB 


25p 


BBZfl 


321p 


BC4 


30p 


IJC5C1T 


3Sp 


-■.I; IjiIi: 


£1-10 


BCA4 


27|p 


BCA7 


S2ip 


liCBC 


27 Ip 


*;ci»;oa£i-is 


BC07 


4Sp 


BCHfi 


5Sp 


BCLO 


SOp 


(5C^'4 


62ip 


BCY5 


40p 


BCY7 


SOp 


BDJ 


40p 


>ilx'-i 


67ip 


SSKO 


4S!p 


BOQGB 


SOp 


BDS4 


75p 


■;i-:a" 


&5p 


HEH7 


32>p 



SEJ7 

BEW6 

6F1 

6F8 

6F6C 

BFU 

11F12 

SF13 

6F14 

CFI5 

6FJ8 

SF22 

6F23 

SP24 

6F25 

BE2fi 

6F2S 

6F29 

6F30 

BJ4 

BJ3GT 



fiK7 

BK8G 

BK23 

6K25 

64BGT 

61-7 

BL18 

6LD20 

SN7GT 

BP1 

6P25 

BP28 

GQ7 

6R7G 

B32 

US 4 A 

68A7 

BSG7 

63 J 7 



3Sp 
60p 
70p 
40p 
25p 
32*p 
22lp 
SSp 
SOp 
SSp 
40p 
32(p 
77(p 
67*p 
75p 
3Sp 
70p 
32tp 
35p 
47 4p 
SOp 
42!p 
SOp 
32-p 
30p 
SOp 
75p 
4Sp 
32ip 
SOp 
32jp 
35p 
SOp 
£1-05 
62 Ip 
37*P 
S5p 
40p 
SSp 
37ip 
32!p 
37 4p 



(5SK7 

CSLTUT 

flSN7(;T 

tiSQ7 

SSR7 

8T8 

6U4GT 

6U8 

GYSGT 

6X4 

BX5GT 

BX8 

6Y6G 

7V4 

9BWS 

10C2 

10D1 

10D2 

10F1 

10F9 

10F18 

10T.1 

10LO11 

r.'f'U-: 

10P14 

12AB5 

J2ACB 

12 A DO 

I3A19 

12AQ5 

12 ATS 

12AU6 

12AV6 

T2AV7 

12A\7 

12AY7 

12B4A 

12BA6 

12BA7 



32!p 
32 1 p 
30p 
40p 
37 ip 

3Sp 
3B(p 
2Sp 
27Jp 
SSp 
SOp 
SOp 
42)p 
SOp 
40p 
40p 



12BEB 

12BH7 

J2BY7 

12 K 5 

19K76T 

19QT6 

12SC7 

129 G 7 

I2SH7 

12SJ7 

123 K7 

123L7GT 

123N7GT 

123Q7 

12»R7 

1437 

20D1 

20L1 

20 PI 

20P3 

20P4 

20P5 

25CS 

25LfiGT 

2 52 4 CI 

ISZfiOT 

30A5 

J0AE3 

3003 5 

30C17 

30C18 

30FS 

30FL1 

30F1.2 

30FL13 

30FL14 

30L1 

SOL IS 

SOLI 7 

SWtg 

30P18 
30P19 



32 i. 
50D 

sop 

:!;,!> 

asp 
asp 

3Sp 
2ip 
2Sp 
40p 
40 p 
4 Op 
40p 
32;p 
SOP 
4Sp 

ei-oo 

SOP 
SOp 
£100 
£100 
45p 
37ip 
SOp 
SOp 
40p 
40p 
75p 
SOp 
7ftp 
SSp 
75p 
92iP 
SOp 
77JP 
45p 
SSp 
SSp 
SOp 
SSp 
75p 



snPLi 

30 PL! 3 

30PL14 

38 A 3 

35 A 5 

33B3 

35C5 

35 1 W 

:.M.'HiT 

8§W4 

3SZ3 

WS4G 

35ZSGT 

S0A5 

■"I'Jil-". 

90CS 

50L6GT 
83 A 1 
!«A2 
90 A U 
D0C1 
SOCU 

14(17 

811A 

6 ISA 

813 

666A 

S642 

6080 

6146 



77 jp 
SOp 
SSp 
SOp 
55p 
S5p 
SSp 
65p 
47Jp 
2Sp 
SSp 
25p 
374p 
SSp 
3Sp 
35p 
40p 
SOp 
37 Ip 
£2-40 
SOp 
£128 
47SP 
£150 
£3 25 
£375 
7 Op 
SOp 
£1-37) 
£1 50 



CATHODE RAY TUBES 

Sew and Budget tubes made by the lending manufacturers. Guaranteed for 2 years. In the event o[ failure 
under guarantee, replacement is made without the usual time n-asting forms. 



Hew 
£ 



MW36-20 
KWas-91 

MW43-C9Z 

MW43-H0Z 
AW43-80Z 



AW4S-88 

AW47-HO 
AW47-91 
A47 14W 



147 13W 

A47-11W 
A47-26W 
A47-26 , W7R 



Budget 

£ 
£450 
£4-50 



CRM171 

CBM172 

CRM173 

CME17U2 

CM El 703 

CME1TW 

C17AA 

C17AF 

t mv: 1 7"') 

A 47 14W 
(..ME 1 1101 
CMi-:i!!ii2 
CM El 903 
C19AH 
CME190C 
CME1005 
D1K I Hi.., 
CME191SB 



£6 60 


£4-52* 


£6 60 


£*-62i 


£6 SO 


*4-82t 


£6-60 


£4-621 


£3 60 


£4-62i 


£6 30 


£4-82r 


£660 


£4-82' 


£6-60 


£4 62) 



£5-95 

£5-95 
£5-95 
£5 95 
£5-95 
£10 27* 
£S S6s 
£SB6i 
£S 33 1 



£4-87 
£4 37 

£4-87 
£4-87 

£4-87 
£3 50 
£7 00 
£7-75 



Type 

AJO-120W/R 

AW53-S0 

AW53 U- 

AW59-91I 

AW39-91 

A59-15W 



£10 85 
£8 93i 
£8 93j 



turn 

A59-11W 

A59-EW caotassa £is ss 

499-16W OMBS300 £13-86 

AS9-23W CME23",") £12-80 

A5'i- 23W/R £12 SO 

AS1-120W/H CME24i:i £1350 

AB5-11W CME2501 £18-60 
COLOUR TUBES 

A49-191X 19 inch £52-50 

A5'i-120X 22 lui-li £57-60 

ASii-llX 25 inch £62-50 

PORTABLE SET TUBES 

TSD217 £1160 

T3D282 £11-80 

A28-14W 19-181 



CME2303 
CME2301 
GME2302 
CM£230a 
CXB2305 
CME230B 
CKS2300 
CME23';m 



Budget 
£ 



£8-25 
£8-25 



£7 20 

£10-971 
£10 97 t 
£10 50 
£3050 
£1160 
£14 -50 



Not 

supplunl 
£7-75 
£3 00 



A discount ol 10',' u is also gl\*en ior the purchase of 3 or more tubes at any one time. 
All types of tubes In stock. Carriage and insurance 75p anywhere in Britain. 



SOp 

40p 

40p 

S5p 

SSp 
£1-00 

SOp 
37 lp 
37fp 

40p 

40p 

m ;Sl L 2 98!P rmi w> 

30p 30FL13 SOp fl 360 £1-26 

48p 30FL14 77 (p 6939 £210 
30p : »L1 «P 7199 76p 

87 *P «KS IfE 7aw el ' M 

60P sopti |5J 7S86 £186 

32jp sopis SSp ^W^ 32tp 

32 ip BS91S 7Sp 9003 SOp 

TRANSISTORISED UHF TUNER UNITS 
NEW AND GUARANTEED FOR 3 MONTHS 
Complete with Aerial Socket and wires (or Radio and Allied TY seta 
but can he used for most makes. 
Continuous Tuning, £4-S0: Push Button, (5 00. 

SERVICE AIDS 
Switch Cleaner, 55p: Switch Cleaner with Lubricant, SSp: Freeza 
62ip. P. & P- 7tp per item. 

PLUGS 
Jack Plugs and Sockets Co- Axial Plugs 

Standard Plugs lfip Belling Lee (or similar type) StP 

Standard Sockets 121p Add 2p per doi. p. <fc p. 

LINE OUTPUT TRANSFORMERS 

£4-75 G.E.C. 2028 £4 -75 

£4 75 G.E.C. 2041 £4-75 

£4 75 G.E.C, 2000 Scries 

£475 Philips 19TG £4-75 

£4-75 Pye Mod. 3fi £4-76 

£4-75 Pye Mod. 40 £4 7S 

£4-75 Thorn 800-850 £4-76 

£4-75 

STYLII— BRITISH MANUFACTURED 
All types m stock. 

Single Tip "S" Up Doable Tip "S" 33p 

Single Tip "D" 37p Double Tip "D" 47p 

"S" ~ Sapphire "D" — Diamond 



G.E.C. 


BT454 


G.E.C. 


BT45B 


G.E.C. 


2010 


G.E.C. 


2013 


G.E.C. 


2014 


G.E.C. 


2013 


G.E.C. 


2043 


G.E.C. 


2043 



CARTRIDGES 



ACQS 
GP7B 

GP91-1SC -I 

GP91-2SC 

GP9K1SC 

Suitable to replao 

TC« 

GP92 

GP93-1 

GP94-1 

GP94-5 

GP95 

GP96 

ACOS 

104 1-10 



/iic. P.T. 
eath 

£0 63 

£105 
£105 
£106 



£1-32 
£124 
11-55 
£1B0 
1 1 24 
£1-57 



£2 09 







/lie. P.T. 




/ n e. P. 7. 


B.S.R. 




each 


ROHETTE 


taeh 


X3M 


BJB 


1 


103 3 B 


30P 


X3H 


s/s 


L £1-50 


106 S/S 


99p 


X5M 


s's 




DC400 S/S 


70p 












9X5M 


s»s 




DC4003C S/S 


70p 


3X5H 


s/a 




105 D/9 


n-ni 


SX3M 


D,'S 


; £2-10 


106 D/3 


£1 -11 1 


SX5H 


D.'S 


DC400 D,'S 


84p 


X4N 


D/a 


£2-50 


DC400SC D/S 


84p 


GOLDRING 




SGNOTONE 




850 




£6-95 


STA D/9 


£135 


G800 




£9-36 




£2 05 


G800E 




£15-0(1 






G800 Super E 


£19 50 


9TAHC D/S 


£2-05 



EX RENTAL TV SETS 

19 inch B.B.C2 Sets £16-50 23 Inch B.B.C.2 sets £18 50. Add £5 00 per set for 

guaranteed working order. Brand new- boxed 20 incb K.B. £5500. Carriage £100. 



SEMICONDUCTORS BRAND NEW MANUFACTURERS MARKINGS NO REMARKED DEVICES 



2N3MKA 

SX697 

2XS98 

8S706 

^S -ml A 

3X9311 

9NU32 

BS1303 

3X1305 

SX 13(1(1 

9X1307 

3X2614 

8X3826 

9X4905 

SX4914 

9X1711 

8X2147 

SN2100 

HXa«4ii 

HX2SHI.". 

SX2926 

i:ir(-J-ri 

Orange 
SX3053 
SN3066 
3X3392 
8X3702 



63piSX 37)14 
20pSX3705 
SSp SX 4061 
13pSX4H02 
13J.SX42M 
28p 3X4291 
33p RCA 
" 40263 
40398 
40438 
AC 107 
AC117 
AC12B 
AC127 
AC128 
AC170 
AC 187 
AU188 
ACY17 
ACY20 
AD140 
AD142 
AD149 
AD I SI 
AD102 
API 02 
AF114 
API 13 



23p AFli>; 
20pAF117 
23p AFU8 



23p 
ISp 
18p 

PA 
J 1 , *- 
VIA 
30p 
SOp 



AF124 
API 23 
AF126 
AF127 
AF139 
AF178 
AF1 79 
AF180 
AF1S1 
20p API 86 



20!! 
SSp 

SU.) 
■:•■, 
2;>n 
40p 
5?)) 

sau 

38p 

5S; 
25p 

2i- 



25piBCll-i 
SSp BC 1 34 
SOp BC 135 
13pBC13S 



» BC137 
20p BC1 38 
ISp BC142 
38p BC143 
45p BC147 
45p BC148 
53p BC149 
43p BC152 



AF23S 
ASY28 
BA144 
BA140 
BA14S 
BA135 
BA100 
BC107 
BC1US 
BC109 
BC113 
BC114 
BC115 
BCH6 
BCI1 6 A 



67p 
43? 

SSp 

P'A 

r'.'A 

23P 
P/A 
P/A 
15p 
ISp 
15p 
2Sp 
SSp 
33p 
S3p 
SSp 



BC158 

BC1S9B 

BC1G9C 

BC171 

BC175 

BC163 

BC164 

BC167 

BC213L 

BCY32 

BCY58 

BCY70 

BD121 

BD123 

BD124 

BD1.11 



33 p 

Mo 
t A 

P I 
!• A 
P A 
30p 

t A 

ISp 
15p 

ISp 
ISp 
ISp 
14p 
15p 
ISp 
28p 
23p 
23p 
29p 
27p 
38p 
23p 
20p 
SSp 
SSp 
63p 



BFU3 

BF117 

BP163 

BF1S7 

BF173 

BF17S 

BF179 

BF160 

BF181 

BF184 

I1K1LH 

BF193 

BF196 

BFI97 

BF2II0 

BF224 

BF225 

BF207 

BFX29 

BF1S1 

BF162 

BF1I53 

BFY19 

BFY50 

BFYS1 

BFY52 

B9X21 

P34BA 



35p 

2Sp 
53P 
35 p 

7^p 
35p 
3.Jp 
2JF 
23p 

::sp 

4 lip 
37p 



40 p 



25pT1343 

48p 

"- DIODES 

RECTIFIERS 



J 

aop 

47p 
35p 
IV A 
PW 
l>5p 
23 p 
23p 
23p 
S3p 
3Sp 
25 p 



1X914 
\ All!' 
BAlna 
BAU5 
BAU4 
BYiOl) 
BY120 
BY127 
BZYH8 

(Scries) 
OA5 



:a f 



OA47 
OA70 
OA79 
OA7I 
OA90 
OA91 
(1A2H2 

P/A 



13p 
8p 
Sp 

t v 

Sp 
8p 
Sp 
lOp 

price 






ADD 3p PER ITEM FOR POST & PACKING FOR ORDERS UNDER 24 PIECES 



TERMS. CASH WITH ORDER ONLY. POST & PACKING PAYABLE ON 
ORDERS UP TO £6-00, AFTER THAT FREE EXCEPT C.R.T.'s. 




Thermistor Th501 is mounted on the heatsink of Tr512/Tr513. 



The type of amplifier described above is thus similar 
in terms of output power and sound quality to the 
majority of audio amplifiers in domestic television re- 
ceivers. If a large loudspeaker is used reasonably good 
results will be obtained, but probably not good enough 
to satisfy the Hi-Fi enthusiast. The main problem is 
that the amplifier has insufficient overdrive capability 
—when the volume is set to give a reasonable listen- 
ing level the high -amplitude transients in the audio 
signal are likely to be clipped, resulting in distortion. 

High-quality Circuit 

The amplifier circuit shown in Fig. 2 provides the 
ultimate answer. Despite its complexity this amplifier 
is remarkably well-behaved. It sets up its own mid- 
point bias and quiescent current automatically, de- 
livers 5W r.m.s. into a 3Q loudspeaker (15V supply) 
or 20W with a 30V supply and has very low distortion 
figures, typically less than 0.1%. Separate bass and 
treble controls are provided, each allowing more than 




-M 



30 



SOD 



10000 



30000 100000 
Hog seal*) 



1000 3000 

Frequency (Hz) 

Fig. 3: Frequency response of the high-quality ten- 
transistor circuit with the tone controls fitted. (Measured 
at 80% of maximum output.) 



12dB lift and cut. A graph of the frequency response 
of the amplifier is shown in Fig. 3 while Table 1 com- 
pares its characteristics with those of the first ampli- 
fier described. 

The operation of the circuit is as follows. The audio 
signal is selected by RLY50I and passes through the 
volume control to the base of Tr504. R509 is not 
capacitively decoupled to chassis so the voltage gain 
of Tr504 is given approximately by the value of R508 
divided by the value of R509 (i.e. x 4) while the am- 
plification is very linear due to the high inherent level 
of negative feedback. The amplified voltage at the 
collector of Tr504 then passes via the tone control 
network to Tr505. 

Consider next the d.c. operating conditions of the 
output amplifier {Tr505 to Tr513): a proportion of 
the mid-point voltage at the junction of the emitters 
of Tr512 and Tr513 is applied to the base of Tr506 
while a fixed bias derived from the potential divider 
R514, R515, R516 and R517 is applied to the base of 
Tr505. Tr505 and Tr506 act as a comparator circuit, 
any difference in the base voltages of these two tran- 
sistors appearing as an error voltage across R518. 
This error voltage is further amplified by Tr509, the 
collector voltage of which directly determines the mid- 
point voltage of the output transistors Tr512 and 
Tr513. By suitable selection of bias resistors the mid- 
point may be arranged to be exactly half the supply 
voltage regardless of the actual level of the supply 
voltage. Any drift is automatically compensated. The 



Table 2 


: Complementary 


transistors 


for use 


with 


positive supply voltage. 


Rep/ace 






By 


BC157 






BC147 


AC128 






AC176 


AC1 76 






AC128 


BC147 






BC157 


BD132 






BD131 


BD131 






BD132 



29 



it components list 



Resistors : 

R501 IkH R505 

R502 47kH R506 

R503 0-5 Q1W R507 

R504 0'5H1W R508 

Potentiometers : 

VR501 10kfilog. 

Capacitors : 

C501 10ftF15V E 

C502 10f*F15VE 

C503 500mF15VE 

C504 0-1 /*F PE 

C506 10^F15VE 

C507 500 pF 35 V E 

Semiconductors : 

D501 AA1 20 (Thorn) 
Tr501 BC157 
Tr502 AC128 



22k £1 

4'7kn 

ikn 

3-9kH 



R509 
R510 
R511 
R512 



IkD 

10kil 
2-2kQ 

1 ok a 



R513 
R514 
R515 
R516 



47k fi 
22k ii 
15kft 
10kO 



R517 
R518 
R519 
R520 



1 0k a 
1-5ka 

V2kQ 
470 D 



R521 
R522 
R523 
R524 



56kH 
56 Q 
220 O 
150 



R525 22k H 
R526 680O 
i/JW 5% unless 
otherwise stated 



VR502 25kfi lin. 



C508 
C509 
C510 
C511 
C512 
C513 



0-02 fxf PE 
0'18|*F PE 
1200pF PE 
6800pF PE 
500 ^F 35V E 
1 /*F 1 5V E 



VR503 100k ill in. 



C514 470pF P 

C515 16/ixF25VE 

C516 1000pF PE 

C517 33pF P 

C518 33pF P 

C519 500 M F35VE 



VR504 100kQlin. 



C520 002fiFPE 

C521 1000mF35VE 

C522 1000pF PE 

E electrolytic ; P polystyrene ; 

PE 160V polyester. 



Tr503 AC176 
Tr504 BC157 
Tr505 BC157 



Tr506 BC1 57 
Tr507 8C157 
Tr508 BC157 



Miscellaneous: 

RLY501 Omron MH2, d.p.c.o. relay (Home Radio). 



Tr509 BC147 Tr512 BD131 

Tr510 BC157 Tr513 BD132 

Tr511 BC147 Th501 VA1038 



Heatsink(s), silicone grease, etc. 



quiescent current in the output transistors is deter- 
mined by the voltage drop across R523 and this is 
itself determined by the collector current of Tr508. 
Tr507 and Tr508 form a constant-current source, thus 
providing a constant voltage across R523 and stabili- 
sation of quiescent current over a wide range of supply 
voltages. A thermistor (Th501) stabilises the quiescent 
current against changes in temperature, 

AC Operation 

The a.C. operation of the amplifier is rather com- 
plicated. Signals of opposite phase are produced at 
the collector and emitter of Tr505. Tr509 provides 
voltage amplification of Tr505's collector signal, but 
Tr508 does not amplify the emitter signal ; any change 
in voltage at the base of Tr508 is immediately sup- 
pressed by a change in the conduction of Tr507. The 
base of Tr508 is thus a virtual earth. We may consider 
the collector impedance of Tr508 as a variable resistor 
of about 1,00011 connected between the base of Tr511 
and earth, its resistance varying to maintain a constant 
current in R523. The amplified a.c. signal at the 
collector of Tr509 thus appears at both sides of R523 : 
for the negative-going part of the waveform Tr510 
and Tr513 conduct, while for the positive-going part 
Tr5Il and Tr512 conduct. Comparing this circuit 
with that shown in Fig. 1, Tr509 takes the place of 
Tr501 with Tr510/Tr513 and Tr511/Tr512 replacing 
Tr502 and Tr503: R523 replaces D501, with the bias 
stabilising action of the diode undertaken by Tr507 
and Tr508. The final amplified signal appears at the 
emitters of Tr512 and Tr513 and is coupled by C521 
to the loudspeaker. 

A.C. negative feedback is applied to the base of 
Tr506, the magnitude of the feedback being deter- 
mined by the a.c. potential divider R525, R520. The 
exceptionally low distortion figures obtainable from 
the amplifier are due partly to this a.c. feedback and 
partly to the use of Tr507 and Tr508 as a constant- 
current source. A IV p-p input to RLY501 will drive 



the amplifier to full output with a 15V supply while 
a 2V p-p input is required for full output with a 30V 
supply. The amplifier is thus fully compatible with the 
sound i.f. circuits described earlier in this series. 

Layout and Construction 

The layout for either amplifier is not critical pro- 
vided the input and output leads are kept well apart. 
It is suggested that the amplifiers are built on paxolin 
pinboard — it is possible to lay the amplifier out exactly 
as it appears in the theoretical circuit diagram. In the 
prototype receiver the entire amplifier is mounted on 
the receiver's control panel, thus permitting the use 
of very short leads to the volume and tone controls. 
Signal-carrying leads of any appreciable length should 
be made up with screened cable. The amplifier earth 
is connected to the main chassis through heavy-duty 
copper braid. RLY501 may most conveniently be 
mounted on the main chassis adjacent to the sound 
i.f. amplifiers: in single-standard receivers it is of 
course omitted. The tone controls in Fig. 2 are op- 
tional : if they are not required it is possible to connect 
together points P and Q on the circuit diagram leaving 
out the intermediate circuitry (Tr504 etc.). 

With both amplifiers heatsinks will be required for 
the output transistors. For the amplifier in Fig. 1 
copper clips each about 2 sq. cm. in area will be 
sufficient for Tr502 and Tr503 so long as the loud- 
speaker impedance is not less than ISO. If a 3fi 
loudspeaker is used the copper clips should be bolted 
to a beavy-duty finned heatsink. No electrical in- 
sulation is required between the cans of these tran- 
sistors. All thermal conduction interfaces (i.e. the 
transistor cans and the side of the copper clips bolted 
to the heatsink) should be given a liberal coating of 
silicone grease : this is most important if thermal run- 
away is to be prevented. Ideally D501 should be 
mounted in thermal contact with the heatsink used 
for the output transistors. 

For the amplifier shown in Fig. 2 a 5cm. x 10cm. 






30 







US5ES3B 

TELEUISIOn 



r A CLOSER LOOK AT PAL 

The basic principles of the PAL system are now 
generally understood. There is however a good 
deat more than meets the eye to the system. So 
next month we are starting a new series in 
which we shall be investigating the system in 
greater detail than previously. The account will 
be descriptive, not a fog of formulae ! 

CONSTRUCTORS' CIRCUITS 

Next month we turn to the line timebase. A 
choice of transistor or valve line oscillator 
circuits, both with flywheel synchronisation, and 
a line output stage with optional stabilisation and 
optional solid-state e.h.t. and boost rectifier 
circuits will be given. 

THE TELDEC SYSTEM 

With the first demonstration of the Teldec system 
in colour at the recent international Berlin Radio 
Exhibition this remarkable disc videorecording 
system is again in the news. A full account of 
the mechanics of the system will be given next 
month. 

RUSSIAN TV RECEIVERS 

There are many novel and unusual features in 
the Temp single-standard receivers manu- 
factured in the USSR and now being widely 
distributed in the UK. For example, an external 
definition control varies the vision i.f. response 
by means of a varicap diode, the line blocking 
oscillator transformer has an adjustable feed-in 
point for optimum a.f.c, automatic brightness 
control is incorporated in the video output stage 
and amplified negative feedback is used in the 
field output stage. We shall be taking a detailed 
look at this interesting chassis. 

PLUS ALL THE REGULAR FEATURES 



ORDER YOUR COPY ON THE FORM BELOW 



(Name of Newsagent) 

Please reser we! deliver the DECEMBER Issue of 
TELEVISION {20p), on sale NOVEMBER 22. 
and continue every month until further notice. 



NAME 



ADDRESS 



black finned heatsink will suffice for output powers 
up to 20W. If both output transistors (Tr512 and 
Tr513) are bolted to the same heatsink a mica washer 
should be placed between the metal side of each tran- 
sistor and the heatsink. Apply plenty of silicone 
grease to both sides of the mica washers. Alternatively 
the transistors may be bolted without mica washers to 
two separate heatsinks electrically isolated from each 
other. The thermistor Th501 should be clipped on to 
the heatsink (or one of the heatsinks if two are used). 
It is advisable to insulate the thermistor from the 
heatsink by sandwiching it between two slices of mica 
washer liberally coated with silicone grease. 

Setting Up 

To set up the three -transistor amplifier turn the 
volume control to minimum, connect a voltmeter be- 
tween the junction of R503 and R504 and chassis 
and apply —15V to the supply rail of the amplifier. 
Set VR502 to give a reading of 7,5V on the meter. If 
an oscilloscope is available it is better to set VR502 
as follows. Inject a 1kHz sinewave signal at the base 
of Tr501 and monitor the output across the loud- 
speaker with an oscilloscope. Increase the level of the 
input signal until clipping occurs, and adjust VR502 so 
that the clipping is symmetrical at the top and bottom 
of the sinewave. The quiescent (zero signal) current 
of the amplifier should be between 10mA and 20mA. 
This is finely set by the voltage drop across D501 : it 
is most important that this type of diode is used other- 
wise the quiescent current will be far too large. 

The ten-transistor amplifier circuit (Fig. 2) requires 
no setting-up adjustment but if any problems arise it 
should be possible to determine the cause of the fault 
by measuring the voltages shown at various points in 
the circuit. In the event of failure of either or both 
output transistors (due perhaps to a short-circuited 
loudspeaker) it is advisable to replace Tr510, Tr511, 
Tr512 and Tr5l3. The level of quiescent current can 
if necessary be finely adjusted by a small change in 
the value of R522. 

General Points 

The loudspeaker used with either amplifier should 
be as large as the receiver cabinet permits. It is pos- 
sible to use more than one loudspeaker, with series or 
parallel connection, but the total impedance presented 
to the output of either amplifier should not he less 
than 3ii. External loudspeakers may easily and safely 
be connected as the receiver has an earthed chassis. 
The use of an electrostatic loudspeaker is not recom- 
mended with the ten-transistor amplifier as it tends 
towards instability when driving this type of capacitive 
load. 

Both amplifiers may be converted to operate from 
a positive supply voltage if required. D501 and all 
electrolytic capacitors must be reversed in polarity 
and each transistor replaced by its complement (see 
Table 2), The circuits are shown for use with a nega- 
tive rail because this was the most suitable supply 
voltage available in the prototype receiver. 

The amplifier circuit shown in Fig. 2 is ideally suited 
for use as a general-purpose Hi-Fi amplifier. When 
used with a record or tape deck a correctly equalised 
preamplifier is necessary giving at least 2V p-p output 
into 10kn. Further details of such a preamplifier can 
be found in the Mullard Book of Transistor Circuits. 
NEXT MONTH A DUAL-STANDARD LINE TIMEBASE 






31 



fP 

Ud 




CHROMINANCE CIRCUITS 

The chroma signal is present with the Y signal at the 
output of the vision detector and in receivers using 
a common vision detector for both signals the chroma 
signal is filtered from the Y signal by a high-pass 
coupling to the chroma bandpass amplifier channel. 
It will be recalled that the chroma signal is removed 
in the Y channel by a chroma trap. 



Chroma Bandpass Amplifiers 

The colour decoder starts with the chroma bandpass 
amplifier channel which is an important section of 
the colour receiver : if there is trouble in this section 
the receiver will probably operate in monochrome 
but certainly not in colour. It is called a bandpass 
amplifier because its response characteristics are con- 
trolled in such a way as to pass the sidebands of the 
chroma signal with the least distortion and without 
letting through unwanted adjacent signals. 

Figure 1 shows the positions of the video and sound 
signals in a 625-line channel in terms of frequencies 
relative to the vision carrier. The range of frequencies 
in which we are currently interested is indicated by 
the shading. This is the part of the video spectrum 
where the chroma signals are carried, spreading out 
approximately 1MHz either side of the chroma sub- 
carrier frequency (4-43 MHz). It is the job of the 
chroma bandpass amplifier channel to accept this 
section of the video waveform and to lift it to a level 
suitable for application to the PAL delay line and its 
associated matrix network. Fig. 2 shows the various 
inputs and outputs of the chroma bandpass amplifier 
channel. 



Burst Blanking 

The chroma signal fed to the PAL delay line should 
not only be devoid of video signal from about 3*4MHz 
down to d.c. but should also be clear of the burst 
information. The bursts are therefore extracted from 
the chroma channel at an early stage and processed 
separately. Burst blanking as it is called is subse- 
quently carried out by switching off the chroma 
channel during the burst period. This is done by 
applying a burst blanking pulse to the channel and 
ensures that unwanted signals are not fed to the syn- 





CIRCUITS 

GORDON J. KING 

chronous detectors during the line retrace period. 
Since the average phase of the transmitted burst is 
coincident with the 180-degree - U chroma axis (see 
last month), corresponding to a yellowish-green hue, 
a vertical line display of this colour at the left of the 
picture would be likely to result should the burst get 
through to the synchronous detectors. 



Automatic Chrominance Control 

Most colour receivers incorporate automatic chroma 
control (a.c.c.) which is a form of a.g.c. in the chroma 
channel. The purpose of this is to hold steady the 
relative amplitudes of the chroma and luminance 
signals under varying conditions of propagation and 
during the normal operational drift of the receiver 
circuits. The chroma signal itself cannot be utilised 
to derive this control bias, which is generally applied 
to an early stage in the chroma bandpass amplifier 
channel, since its value is continually changing 
with the varying colouring information. Since the 
burst signal is not modulated however the a.c.c. bias 
can be derived from this signal either directly or 
indirectly from the ripple signal resulting from the 
burst swings. 

Manual Chrominance Control 

Provision for manual gain control in the chroma 
amplifier channel is also necessary to allow the 
amplitude of the chroma signal fed to the synchronous 
detectors — and hence the saturation of the display — 
to be adjusted. In some sets electrical or mechanical 
ganging of the contrast and colour controls is adopted 
so that the chroma/ luminance ratio holds fairly 
constant as the colour control is adjusted. 

Colour Killer 

One stage of the chroma amplifier channel is 
deliberately biased to cut-off in the absence of a 
colour signal. A switch-on bias for this stage is how- 
ever obtained from the bursts— or from the ident 
signal derived from them — when the transmission 
carries colour information. This technique ensures 
that the chroma channel is inactive during mono- 

Cotogr Colour 
killer control 



From vision^ 
dettitor 



]_£. 



Chroma bandpass amplifier 
channtl 



I Outpul 



_ To PAL 
delay tlrw 



Output to Burst 
ACC burst Wanking 
bias chanrwl 



Fig. 1: U.H.F, television channel spectrum, showing the 
portion occupied by the chroma signal. 



Fig. 2: Black diagram of the chroma channel. 



32 



V5k 




Bandpass coupling 




ejector 



Fig. 4 (above); The response 
of the circuit shown in Fig. 3. 



Fig. 3 (ieft); Chroma channel 
used in early Decca dual- 
standard colour receivers. 



chrome transmissions: without it random video signals 
and noise focused ± 1 MHz relative to the subcarrier 
frequency would tend to introduce disconcerting flecks 
of colour on a black-and-white picture. It is from this 
"colour killing' 1 action that the circuit takes its name: 
it is however really a "colour activator" system since 
the controlled stage is basically cut-off, being biased 
on by the rectified and smoothed burst signal. 



the spectrum from about 3-4MHz down to the vision 
carrier and the 6MHz rejector which puts a sharp 
notch in the response at the other side of the passband. 
The rejector and the primary and secondary of Tl 
are adjusted to secure the response shown in Fig. 4. 
A sweep generator with marker frequencies and an 
oscilloscope are required for this setting up. The take 
off to the burst channel is at Trl collector. 



Simple Chrominance Channel 

A fairly simple chroma amplifier channel— used in 
Decca dual-standard models — is shown in Fig. 3. This 
particular channel is not equipped with a.c.c. so the 
only controls involved are the colour killer, manual 
colour and burst blanking. The input signal is 
obtained from the vision detector via a video phase 
splitter (common dual-standard practice) and thus 
contains luminance as well as chroma information. 
The luminance signal is eliminated by the input high- 
pass filter CI /LI so that Trl base receives only the 
chroma signal. This appears amplified across the 
primary of the bandpass coupling transformer Tl and 
is conveyed via the secondary winding to Tr2 base by 
way of the colour control which acts as a simple signal 
potentiometer. Transformer T2 couples Tr2 to the 
PAL delay line circuit. 

B ndpass Response 

An important feature is the 6MHz rejector in Trl 
emitter circuit. This is required because the upper 
passband of the channel cannot be defined sufficiently 
by the coupling transformers so that without the 
rejector the chroma channel would pass on to the 
succeeding circuits any components of the 6MHz 
intercarrier signal present. The required bandwidth is 
thus obtained by the high-pass filter which rolls-off 



ACC 
reel HI «r 

/ 
Burst D1 
signal BA130 XMk 

* Mj wvi 

.0-1 




Fig. 5: Decca a.c.c. circuit. 



Colour Killer Action 

The colour killing and burst blanking actions are 
both carried out in stage Tr2. The colour killer works 
in the base circuit. The base bias potential-divider 
resistors are R3 and R4 which are linked to Tr2 base 
by D3 and the colour control. On monochrome 
reception the positive potential at D3 cathode switches 
D3 off, removing the base bias from Tr2. When a 
colour signal is being received the ident signal pro- 
duced from the bursts is rectified by Dl and a positive 
potential develops across C3 to forward bias D3 and 
thus link Tr2 to its base bias network, Tr2 is thus 
brought into conduction and passes the chroma signal 
to the delay line. 

Burst Blanking System 

The burst blanking works in the emitter circuit of 
Tr2 and is similar to the line and field flyback blanking 
carried out in the luminance channel of sets using 
colour-difference tube drive. Positive-going pulses 
from the line output transformer are applied to Tr2 
emitter via D2 and R5, switching Tr2 off during the 
line sync pulse and burst period. -The diode deletes 
negative overshoots. 

Decca ACC Circuit 

Burst blanking and colour killing are carried out in 
various ways by the different setmakers: before 
looking at some alternative techniques however we will 
take a look at the simple a.cx. system used in Mark II 
dual-standard Decca receivers. This employs an extra 
transistor stage (Trl) in the chroma channel as shown 
in Fig. 5. As before the signal from the vision detector 
is fed to the base of the first chroma amplifier (Tr2) 
with the high-pass filter still active but now the bottom 
arm of the base potential-divider consists of a variable 
resistor VR1, In the absence of a colour signal this 
is adjusted so that Tr2 runs at maximum gain. When 
a colour signal is present the bursts are rectified by the 



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C400 


Mp 


OCB2 


ISp 


BC183L 


lOp 


BFI7B 


4Sp 


C407 


Up 


OC82D 


ISp 


BCI84 


Up 


BFI79 


SOp 


C424 


Up 


OC63 


J?" 


BC184L 


Up 


BFIBO 


JOP 


C425 


40p 


OCB4 


ZOp 


BCI86 


Up 


BFI8I 


JOp 


C426 


Mp 


OCI39 


ISp 


BCI87 


2T& 


BFI82 


JOp 


C«B 


ZOp 


OCI40 


ITp 


BC207 


Up 


8FI83 


JOp 


C44I 


Up 


OCI70 


Up 


BC209 


Up 


SFI84 


Up 


C442 


Up 


OCI7I 


Up 


BC209 


lip 


BFI6S 


JOp 


C444 


ITp 


OC200 


up 


BC2I2L 


lip 


BFI88 


JOp 


C4S0 


ITp 


QOQI 


ZTp 


BC2I3L 


lip 


SFI94 


Up 


C720 


Up 


OCI02 


Z7p 


BC2I3L 


Up 


BFI9S 


24 p 


C7U 


Up 


OC203 


Up 


BC2I4L 


Up 


BFI96 


JOp 


C740 


Up 


OC204 


Up 


BC225 


2Sp 


BFI97 


JSp 


C742 


ITp 


OC20S 


ISp 


BC226 


ISp 


BF20O 


45p 


C744 


Up 


OC3Q9 


ISp 


BC317 


lip 


BF27.2 


•Op 


C760 


Up 


P346A 


Up 


BC3I8 


Up 


BF257 


ISp 


C762 


Up 


P397 


4Sp 


SCI 19 


Up 


BF270 


Up 


C764 


Up 


OCP7I 


43p 


BCY3Q 


20c 


BF27I 


Up 


EC401 


ISp 


OKP12 


4Jp 



ORP60 

OftPel 

STI40 

STI4I 

TIS43 

UT46 

V405A 

V4I0A 

2G301 

2G302 

2G303 

2G304 

2G306 

2G308 

2GJ09 

2G339 

2G339A 

2G344 

2G345 

2G37I 

2G37IB 

2G374 

2G377 

2G378 

2G3S2 

2G40I 

2G4I4 

2G4I7 

2N388 

2N3S8A 

2N404 

2N404A 

2NS24 

2NS27 

2N696 

2N697 

2N69B 

2N699 

2N706 

2 N 706 A 

2N708 

IN709 

2N7II 

2Nul7 

2N7I8 

2N7I8A 

2N726 

2N727 

2N74J 

2N744 

2N9I4 



40p 2N9I8 Mp 2N27I4 ISp 2N3704 

40p 2N929 Up ZNZ904 Up 2 N 370 S 

Up 2N930 Up 2N2904A Mp 2N3706 

ITp 2NII3I Mp 2NZ905 Up 2N3707 

40p 2NM32 22p 2N2905A Mp 2N3708 

ITp 2NI302 I7p 2N2906 Up 2N3709 

Up 2NI303 Up 2N2906A17p 2 N 37 10 

45p 2NI304 Mp 2N2907 Up 2N37II 

Up 2NI30S Mp 2 N 2907 A JOp 2N3SI9 

Up 2NII06 Up 2N2923 Up 2N3S20 

l*p 2NI307 22p 2N2924 Up 2M3903 

Mp 2NI308 ZTp 2N1925 Up ZN3904 

JSp 2NI309 ZTp 2N2926 2N390S 

JSp IN 161 3 ITp (G) Up 2N3906 

JSp 2NI7II ZOp ZN2926 2N40S8 

Up 2NI889 JSp (Y) Mp 2N4059 

ISp 2NIS90 45p 2N2926 2N4060 

ISp 2NI893 ITp (O) lOp 2N406I 

ISp 2N2I60 Mp 2N3OI0 Mp 2N4062 

Up 2N2147 TSp 2N30I I Mp 2N5I72 

lOp 2N2I48 Mp 2N3053 Mp 2N5459 

ITp 2N2I92 Mp 2N3054 Mp 25034 

ZTp 2N2I93 Mp 2N3055 63 p 2S30I 

ISp 2M2I94 ZTp 2N339I ITp 2S302A 

• Sp 2N22I7 ZOp 2N339IA10p 2S302 

Mp 2N22I8 Up 2N3392 ITp 2S303 

Mp 2N22I9 ZTp 2N3393 ISp 25304 

ZSp 2N2Z20 Up 2N3394 ISp 2S305 

Mp 2N222I Up 2N339S 20p IS 306 

Mp 7 N 2222 ZTp 2 N 3402 Up 2S307 

Up 2N2368 ITp 2N3403 Up 2S32I 

Mp 2N2369 ISp 2N3404 Up 2S322 

SSp 2N2369A ISp 2 N 3405 4Sp 2S322A 

60 p 2N24II Mp 2N34I4 Mp 2S32I 

Up 2N24I2 Mp 2N34I5 Mp 2S324 

ISp 2N26I6 SSp 2N34I7 ITp 2S325 

Z4p 2N27 1 I Up 2N3S25 74p 2S326 

SSp 2N27I2 Up 2N3702 lip 2S327 

Tp 2N27I4 Up 2N3703 Up 

■p 
Up 

4Sp AAM9 

40p AAIM 

4Zp BAII6 

Z4p BAI26 

Mp BY 100 

ZTp BYIOI 

ZTp BYIOS 

ITp BY II 4 

17p BY I 26 

ITp BYI27 



DIODES & RECTIFIERS 
•p BY 130 Up OAIO 
tp BYZIO JSp OA47 



Up BYZ I I 

Up BYZ 12 



Up OA70 
Mp QA79 



Up BYZ 1 3 Up OABI 

Up BYZ 1 6 JSp OAB5 

Up BYZI7 JSp OA90 

lip BYZIB JOp OA9I 

ISp BYZI9 Up OA95 

Up OA5 Up OA200 



Up 
Up 
IZp 
Up 

•p 
•p 

I Op 
I Op 



Up 

ZTp 

Up 

Wp 

Up 

lOp 

Up 

IZp 

Up 

Up 

4Jp 

TSp 

SOp 

45p 

4Sp 

«Op 

£1 10 

£1 

£1 li 

£1-10 

*0p 

Mp 

4Sp 

Mp 

£1 10 

£1 M 

£1 10 

£1 10 



21p 
Tp 
Tp 
■p 

Tp 

*P 
Tp 
Tp 

6p 



74 Series T.T.L. I.C-s 

DOWN AGAIN IN PRICE 



Check our 74 Series List before y»u buj- 8ny Iff*. Our 
ure the lowest panslhli. Ail devices tx -stock. 
Full &t>ecJtlcjUton euaratitee*!. 

BI-PAK 

SimilAr Trpes to ; Deierlptioa 



%» 



Order Ho, 



BP04 - 7404 
BPflS = 7405 
BP10 - 7410 
BP13 = 741 a 
BP20 - 7490 
BP3U - 7430 
BP40 = 7440 
BP4I - 7441 
BP42 = 7442 



BP48 - 7+48 
BP50 = 7450 
BP51 = 7451 



Quail. -2-lnput SAND (?aie 

Quad. 2-input pntttn KAHD pile (with 

open collector output) . - 
Quad. H-inpat poslHv-e NOR gates 
Quad. 2-input ponttlve NASD gates (with 

open collector output) . . . • 0'15 

Hes Inverters . . . . - ■ 0"15 

Hes Inverter (with open-cu Hector output) 015 
Triple 3-input positive SAND gutes . . 0-16 
Dual 4 -input Suhmiit trigger 
DuaI 4-input positive NASD gates 
S-input positive NAXD gates 
13uiil 4-input positive NASD buffers 
BCD to decimal nixie driver 
BCD to decimal decuder (4-10 lines, 1 of 

10) 

BCDito-seven-segment decc-iler driver . . 
BCD-to-seveti segment decoder drivers 

(15V outputs) 

BCD-to-seveti-segment decoder driver . . 
BxpndAbh dual 2. input and-or-lnvert . . 
Dual 2-wide 2-lnput SASD-or-invert 

gates 

Qnad. 2-input expandable SANl)-or- 

Invert . . ■ ■ •• 



Prie* and qty. prioei 

1-24 25-69 100 up 

tp 

014 



1° 

015 



*P 
018 



15 
015 



29 
015 
015 
015 
0-87 

0-67 
2 00 

0-ST 
0-97 
015 



014 

814 

014 
014 
014 
14 

028 
14 

14 
014 
064 

0-64 
1-75 

B4 
8 94 
14 



12 
012 

12 
12 
OIZ 
12 
24 
012 
012 
012 
0-58 

068 
1-60 

88 
0-88 
012 



015 014 12 

016 014 012 



HI' 5 4 
BPfiO - 
BP70 - 
BP72 - 
IU'7;: 
Ul'T-; 
BP75 
BP78 - 
BPS0 - 
Rt'Wl - 
BP82 - 
BP«» - 
BP80 - 
BPt'O 
BP91 ™ 
BP92 - 
Bl'93 
Bt'94 
BP95 - 
BPStl - 
BP100 
BP104 
BP105 
BP107 

Brno 

BPtll 
BP118 

BPI19 
BP12I 
BP141 
BP145 
BP150 
BP151 
BP153 
BP154 



7454 
7480 
7470 



7475 
74711 
7480 
7481 

748a 

7483 

7486 

7490 

7491 

J492 

749.1 

7494 

7493 

7498 
74100 
74104 
74150 
74107 
74110 
74111 
7411K 
74119 
74121 
74141 
74145 
74150 
74151 
74153 
74154 



ANOTHER BI-PAK FIRST I 

THE NEW S.G.S. EA 1000 AUDIO AMPLIFIER MODULE 
* Guaranteed not less than 3 Watts RMS. 



j€ 



xs. 



sV< 



Especially designed by S.G.S. incorporating their proven Linear 
1,C. Audio Amp. TA/621 providing unlimited application! for the 
enthusiast in the construction of radios, record players, Audio and 
Stereo units. Also ideal for intercom systems, monitoring applica- 
tions and phone answering machines. OTHER USES: portable ^^Hp^ 
applications where supply raili as few as 9V are of prime importance, ^r 

• Typical Total Harmonic distortion at I watt 
less than I".,. 

* Supply Voltage <Vi) = 24V 15 ohm load. 
Modual Tested and Guaranteed. 
Q ty , |_o £2-63; 10—25 £2-28 Price each 
Larger quantities quoted on request. Full hook-up 
diagrams and complete technical data supplied 
free with each modual or available separately at 
lOp each. 



• Sensitivity 40 mV for I watt, VOLT- 
AGE GAIN 40 dB but can be varied 
up to 73 dB for some applications. 

• Signal to Noise Ratio 85 dB. 

• Frequency response better than 50 Hz 
to 25 KHi for -—3 dB. 

(J) Normal supply Voltage 9 — 24V. 
Suitable for 6 — 16 Ohm loads. 

• Overall Size 1 in. Klin, x i in. 



4-wMe 2-lnput NAND-or-invert gate; 

Dual 4-input expander . . 

Single-phase J -K dip. nop 

Master-alave J-K flip-flop 

Dual master slave J-K flip-flop . . 

Dual D type flip-flop 

Quad, latch 

Dual J-K with pre -set and clear 

Dated full adders 

lfi-bit read -write memory 
2 -bit binary full adders 

Quad, full adder 

Quad. 2-lnput exclusive Nor gates. 

BCD decade counter 

s-bh shift ngbtan 

Dlvide-by-twelve counters 

4-blt binary couivtere 

Dual entry 4-bit ahlf t register . . 

4-blt up-down alUlt register 

5-blt parallel in parallel out shift-register 

Mill bistable latches 

Single J-K flip-flop eqniv. 9000 series 

Single J-K flip-flop equiv. 0001 . . 

Dual nuisler slave flip-flop 

Gates master-slave flip-flop 

Dual data lock-oat flip-flop 

Hex j-ct -reset latches 

Hex set-reset latches. 24 -pin 

Monostable multivibrators 

BCD-to-decima! decoder/driver . . 

BCD-to-decSmat decoder/driver. O'C 

18-blt data selector 

8-tolt data selectors (with strohe) 

Dual 4 -[ I tie-to -1 -line data 

4 to in line decoder 



015 
015 

0-2S 
087 
0-37 

47 
0-43 
0-67 
0-97 
0-97 
110 
0-32 
0-87 
0-87 
0-67 
0-87 
0-77 
0-77 
0-77 
1-76 
0-87 
0-87 
040 
0-56 

1 35 
100 
1-35 
0-87 
0-87 
1-50 
180 
1 00 
ISO 
1-80 



0-14 
14 

28 
0<2o 
0-35 
0-35 
45 
40 
0-84 
0-94 
94 
105 
030 
084 
84 
0-84 
84 
0-74 
0-74 
0-74 
185 
094 
94 
0-38 

53 
115 
095 
1-25 
0-04 
0-84 

1 40 
1-70 
DB5 
110 
170 



012 
012 
024 
024 

0-32 
0-32 
0-42 
0-38 
58 
0-88 
0-88 
095 
28 
058 
78 

58 
0-58 
0-88 
0-68 
0-68 

1 55 
088 
88 
36 
60 
100 
80 
110 
58 
068 
1-30 
1-60 
0-90 
0-95 
1-80 



Alt prices Qiiutttl in new pence Giro No. S88-i 
Please srid all orders direct to warehouse ' 
and dessiatch department 



VBjZiI 



P.O. BOX 6, WARE*- HERTS 

Postage 3nd poking ado tp. ' 

Orerscas add * it ra for airmail u 

Minimum order 50p Cash with order please. 

Guaranteed Satisfaction or Money Back " 



34 



LAWSON BRAND NEW TELEVISION TUBES 

SPECIFICATION: The Lawson range of new television tubes are designed to give superb 
performance, coupled with maximum reliability and very long life. All tubes are the products of 
Britain's major CRT. manufacturers, and each tube Is an exact replacement. Tubes are produced 
to the original specifications but incorporate the very latest design improvements such as: High 
Brightness Maximum ContrastSitver Activated Screens, Micro-Fine Aluminising, Precision Aligned 
Gun Jigging, together with Ultra Hard R.F. High Vacuum Techniques. 




DIRECT REPLACEMENTS FOR MULLARD-MAZDA BRIMAR CEC, ETC. 



A2I-IIW (P) 
A28-14W (P) 
A3I-IBW (P) 
A47-IIW (P) 
A47-13W (T) 
A47-14W(M) 
A47-17W (P) 
A47-I8W (P) 
A47-26W (P) 
A59-I1W (P) 
A59-I2W (P) 
A59-I3W (T) 
A59-14W {T 
A59-I5W (M) 
A59-I4W (T 
AW36-80 (M 
AW43-80 (M 
AW43-8B (M) 
AW43-89 (H 
AW47190 M 



AW47-9I (M) 

MW43-64{M) 

MW43-69(M) 

KW43-80 (M) 

MW52/20{M) 

HW53/80 (M) 

AW47-97 (M) 

AWS3-80 (M) 

AW53-88 (M) 

AW53-89 (M) 

AW59-90 (M) 

AWS9-9I (M) 

CI7/IA 

CI7/SA 

CI7/7A 

CI7/AA 

C17/AF 

CI7/FM 

CI7/5M 



CI9/I0AP (T) 



CI9/AK 
C2I/IA 

a; 7a 

C2I/AA 
C1!/AF 

C21/KM 
C2I/SM 
C23/7A 

C23/I0 
C23/AK 
CME1 ICI 
CME 120 1 
CM El 402 (M) 
CMEI6C1 (P) 
CME 1 602 (P) 
CMEI702 (M) 
CME 1703 (M) 
CME170S (M 
CME 1706 (M) 
CMEI90I (M) 



(M) 
(M) 
(M) 
(M) 

M 

(M) 
(M) 
(M) 
(M) 
(M) 
(P) 
(P) 



CME 1 902 (M) 
CMEI903 (M) 
CME 1 905 (M) 
CME 1 906 (T) 
CME 1908 (M) 
CME2I0I (M) 
CME2I04 (M) 
CME230I (M) 
CME2302 CM) 
CME2303 (M) 
CME230S (P) 
CME2306 (T» 
CME2308 (M) 
CRMI72 (M 
CRMI73 
CRM2I2 
CRM2II 
23SP4 
I71K 
I72K 



I73K 
2I2K 
720SA 

7405A 

7406A 

7502A 

7S03A 

7504A 

760 1 A 

7701 A 

CRMI2I 

MW3I-74(M) 

A50-I20W/R 

m 



(M) 
(M) 
(M> 
(M) 
(M) 
(M) 
(M) 
IM) 

m 
M 

M) 



LAWSON TUBES 

18 CHURCHDOWN ROAD, 
MALVERN, WORCS. 
Malvern 2100 



2 YEARS' GUARANTEE 
FULL TUBE FITTING 
INSTRUCTIONS 

Tubes are despatched day of order 
by passenger train, road or goods 
taking far too tong for customers 
satisfaction. 



REBUILT TUBES 

LAWSON "RED LABEL" CRTS are 

particularly useful where cost is a vital factor, such 
as in older sets or rental use. Lawson "Red Label" 
CRTS are completely rebuilt from selected glass, 
are direct replacements and guaranteed for two 

years. 



17" 
19" 
21" 

23" 
19" 

23" 
19" 

20" 
23" 
1 6" 



(M) 

(M) 

(M) 

(M) 

Twin Panel (T) 

Twin Panel (T) 

Panorama (P) 

Panorama (P) 

Panorama (P) 

Panorama (P) 



Brand 
New 
Tubes 



£625 



C7-Z5 



W-M 



£9 75 



£10 25 



£1550 



£9 38 



£10 50 



i\\ ?5 



£8 50 



Red 

Label 
Rebuilt 



£4 97 ] 

£525 j 



ii2L 



£7 25 



N.A. 



N.A. 



£6-95 



Carr. 

Ins, 
12" - ir 

62p 



20". 23* 
75p 



£7-50 



.££ 



—I 



T.V. 
TUBES 




"VIDEOCHROME" ™v- 

FOR BRILLIANCE & DEFINITION 



17" £5-00 
19" £5-50 
21" £7-00 
23" £7-50 

19" PANORAMA £6-25 
23" PANORAMA £8-25 

CASH OR CHEQUE WITH ORDER 

TRADE SUPPLIED 

ALL TUBES PRECISION REBUILT AT OUR OWN 

FACTORY BY SKILLED CRAFTSMEN • EACH TUBE 

BENCH AND SET TESTED TO A VERY HIGH 

STANDARD BEFORE DESPATCH 

2 YEARS GUARANTEE • FREE 
DELIVERY ANYWHERE IN THE U.K. 

VIDEOCHROME TUBES LTD. 

25 BELLEVUE AVENUE 
RAMSGATE, KENT. Tel. THANET 52914 



VALVES 



SAME DAY SERVICE 

NEW! TESTED 1 GUARANTEED I 



Bet of 4 for tl-OZ. DAF96, DF96, DK98, DL98. 4 tor fl-48. 



IBS 


-sw 


30C1 


-s« 


DT87 


■25 


EL500 


• 8S 


PCL82 


•32 


185 


-22 


30CIB 


M 


DY802 


■3ft 


EHS0 


-41 


FCL83 


■57 


1T4 


•18 


30C17 


m 


EABC80 


•K« 


EH81 


-41 


PCL84 


■34 


384 


-?« 


30C18 


•m 


EAF42 


•6U 


EM84 


-S2 


PCL8B 


■38 


SV4 


•37 


S0F6 


■! f i, 


F.B41 


-SU 


EM8T 


■3d 


PCL88 


■40 


5U4G 


•M 


SQFL] 


■si 


EB91 


■11 


ETfil 


■UK 


PCL88 


U6 


5V4G 


m 


30FL12 


■70 


EBC33 


• 4U 


ET88 


■;»>l 


PCL800 


-75 


BY3GT 


-B6 


30FL14 


■88 


EBC41 


■54 


EZ40 


■43 


PE3STA4 


-77 


BZ4G 


■35 


30L1 


•29 


EBC90 


m 


EZ41 


■43 


PES3RC 


m 


8/30L2 


-S4 


30115 


•57 


EBF80 


■m 


EZ80 


■Bl; 


PFL200 


■53 


6ALB 


• 11 


30L17 


•71 


EBF89 


■aii 


EZ81 


<9 


PL38 


.49 


SAMS 


41 


30F4 


-85 


EOC81 


■17 


GZ30 


-35 


Ftai 


-44 


<!AQK 


■?.?. 


30F12 


•li. 


Ecxaa 


• 20 


GZ32 


■40 


PL81A 


-49 


BATH 


90 


S0F19 


49 


ECC83 


•35 


GZ34 


■48 


PL82 


•31 


6AUB 


•to 


30PL1 


« 


E<X»5 


.a« 


KT41 


■ 77 


FL83 


M 


8BAS 


-80 


S0PE13 


■7B 


ECS3S04 


•SB 


KT81 


•BS 


FL84 


-30 


8BE8 


■PI 


30PL14 


m 


ECF80 


■27 


KT8S 


-78 


PL800 


41 


8BJ6 


■41 


30PL15 


•90 


ECE83 


■*e 


LS319 


• S3 


FLB04 


■ 83 


8BW7 


■5? 


3BL6GT 


•4S 


ECH35 


so 


LN329 


• 72 


PH84 


■36 


6CD6G«.07 


3SW4 


m 


ECH42 


40 


LN339 


-63 


PX.2S 1100 


SF14 


■ 49, 


35Z4GT 


•m 


ECH81 


■?s 


U78 


■87 


PT32 


-55 


6F23 


-88 


807 


.4S 


ECH83 


■40 


P61 


-45 


FT33 


■ 55 


6F25 


■■•,7 


6063 


■ 8? 


£CH*4- 


■ 38 


FABCS0 


■34 


PT81 


■ 25 


8K7G 


•is 


AC/VF2 


■77 


ECLSO 


.30 


FC8B 


■47 


PT8S 


■25 


8K8G 


.17 


B349 


41 


ECL82 


■ 31 


PC88 


■47 


PY8S 


•28 


6Q7G 


■27 


B729 


■6S 


ECL86 


m 


PC96 


■K 


FT88 


•33 


6SN7GT 


■ 30 


OCHS5 


■S7 


EF39 


M 


PC97 


■89 


PY800 


-34 


6VSO 


4d 


CY31 


•30 


EF41 


■BO 


PC9O0 


-33 


FY801 


84 


8V0GT 


■31 


DAF91 


■is. 


EF80 


-Si 5 


POC»4 


-29 


B19 


•39 


8X4 


■23 


EMVM 


m 


EFSS 


■M 


POC8« 


■?7 


E20 


-&K 


6X6GT 


m 


DF83 


■18 


ElsS 


-Rl 


PCC88 


-4? 


1126 


-84 


7B7 


-S3 


DF91 


EFSS 


•M 


POC89 


•46 


U28 


-S8 


10P1S 


•ia 


DF96 


• 38 


EF91 


.13 


FCC189 


• 48 


U47 


-85 


12AT7 


-17 


DH77 


4M 


EF98 


-85 


PCC80S 


■fifl 


U49 


•58 


12AU8 


4M 


BK32 


m 


EF183 


-iW 


FCF80 


4H 


TJBO 


>M 


12AU7 


ia 


DK91 


m 


EF184 


■ 31 


PCF82 


■31 


TTG3 


■31 


1 Li AX 7 


.?,?. 


DK93 


m 


EE90 


•37 


PCF88 


-4.1 


U78 


•M 


19BQ8G 


m 


DE&8 


■SA 


EL33 


•SB 


PCE800 


St 


D191 


■59 


20F2 


-87 


DL35 


• 411 


EL34 


•45 


PCF801 


■30 


T1193 


-4K 


20FS 


• 80 


BL92 


•as 


EL41 


-54 


PCF802 


■ 44 


U2B1 


-M 


20P4 


■w 


DL94 


.37 


ELS4 


• 2$ 


PCF80S 


• 81 


U301 


■38 


26L8GT 


■ 20 


riLSti 


-3R 


EE90 


.--• 


PCF806 


• 56 


U329 


-flfl 


3BU4GT 


•S7 


Drafi 


.i* 


EL9S 


■n 


PCFB08 


-68 


U801 


■98 



I 'ABC SO 

0AF42 

UBC41 

UBF80 

UBF89 

UOC84 

UOC8B 

UCF80 

UCH42 

UCH81 

UCL82 

UCL83 

1JF41 

UP89 

111.41 



UL44 «1-00 
VL84 -ID 



TJM84 
CY41 
UY85 
VP4B 
Z77 
TnuuiitaN 
AC107 
AC127 
AD14» 
AF115 

AFne 

AF117 

AF118 

AF12B 

AF127 

OC26 

OC44 

OC46 

OC71 

OC73 

OC7B 

OC81 

OC81D 

OC82 

OC82D 

OC170 



READERS RADIO 

IS TORQUAY GARDENS, REDBRIOGE, ILFORD, 
ESSEX. Tel. 01.550 7441. 

Foetige on 1 valve 5p, on 2 or more valves Sp per vaivo extra. 
Any parcel insured against damage in trans it 3p extra. 






35 



Input from 2nd stage 
' ot main I F channel 




TACC bias 

Fig. 7: Chrominance i.f., a. ex., detector and bandpass amplifier circuits used in the RBM single-standard colour chassis. 



a.cc rectifier Dl and a positive bias is fed to Trl 
base. This bias overcomes the back -bias tapped from 
VR2 so that Trl is brought into conduction. Current 
thus flows via D2 into Tr2 base circuit, and the 
increased current flowing through VR1 increases the 
positive bias on Tr2 base. The result is forward a.g.c. 
at Tr2 base, reducing the gain of this stage : the system 
provides not less than 6dB of a.cc. 



Improved Blanking 

The Mark II chassis also features improved burst 
blanking based on the use of a two-diode clamp 
circuit with positive- and negative-going drive pulses. 
The circuit is shown in Fig. 6. Trl is the second 
chroma channel transistor and diodes DI and D2 
replace D2 in Fig. 3. The symmetrical diode clamp 
circuit is located between the final coupling trans- 
former and the PAL delay line. During the line fly- 
back period the positive pulse at Dl anode and the 
negative pulse at D2 cathode make both diodes con- 
duct: when this happens any signal at Tl secondary 
is effectively shorted to chassis through CI and C2. 



Chrominance IF Channel 

While it is usual to find the a.cc. operating in the 
chroma channel the RBM chassis used in recent 
Bush and Murphy receivers tackles this in a different 
manner. The design is based on the use of a separate 
chroma detector which is fed from its own i.f. channel 
as shown in Fig. 7. Signal from the main i.f. channel 
is coupled to 2VT8 base through 2C44 while the col- 
lector of this chroma i.f. amplifier transistor drives the 
bandpass-coupled pair 2L17 and 2L18, with top- 



To PAL delay line 



From colour control 




+ pulse -pulse 

Fig. 6: Two- diode burst blanking circuit. 



capacitance coupling provided by 2C47. The signal 
across 2L18 is then coupled via 2C50 to another 
chroma i.f. stage 2VT9 whose collector circuit drives 
the chroma detector 2D 5 from transformer 2L19/2L20. 

Controlled Stage 

The controlled stage is 2VT8 the base bias of which 
is controlled by 2VT7 collector current flowing 
through 2R38 and 2R39 since 2VT8 base is connected 
to the junction of these two resistors through 2R40. 
As the collector current of 2VT7 is dependent on the 
bias at its base it follows that by adjusting 2RV4 the 
bias at the base of both 2VT7 and 2VT8 will alter and 
in this way the gain of the chroma i.f. amplifier 
channel is regulated: 2RV4 is in fact the colour 
control. 

2VT7 makes it possible to apply the a.cc. bias also 
to the i.f. channel. As the circuit shows this bias is 
applied to 2VT7 emitter. The bias is positive and 
increases in value with increasing burst amplitude (it 
is obtained by rectifying the burst signal). As the bias 
increases, the collector current of 2VT7 decreases 
since it is an npn transistor. The reduced voltage drop 
across 2R39 increases the base bias of 2VT8 and its 
gain is reduced through forward a.g.c. action. 

RBM Chrominance Channel 

The chroma channel proper consists of 2VT10 and 
2VTI1 driven from the chroma detector 2D5. The 
detector load is 2R48 and the purpose of choke 2L21 
is to remove unwanted residual i.f. carrier signal. 
Choke 2L22 in series with the load provides the 
required compensation to maintain the response of 
the chroma circuit. Rapid roll-off at the intercarrier 
frequency is provided by the bifilar-T trap 2L23 and 
associated components while the bandpass charac- 
teristic is provided by the top coupled bandpass pair 
2L24 and 2L25. The latter feeds the PAL delay line 
driver via a burst blanking gate, and also the burst 
channel. A degree of response correction is provided 
by the unbypassed part of 2VTll's emitter circuit 
(2R56). 

We shall be looking at the following circuitry which 
includes the colour killing and burst blanking arrange- 
ments next month along with the response characteris- 
tics of this particular chassis. 







crpn nn 




Unfortunately Sporadic E conditions declined some- 
what during the latter part of August following an excel- 
lent first week. Indeed the signals encountered during the 
first week were some of the best of the present season. 
After August 8th conditions fell off but began to pick up 
from the 25th — certainly as far as Sp.E is concerned. 
Tropospherics were above average in the middle of the 
month and again towards the 26th, giving the various 
v.h.f. /u.h.f. ORTF reception from Northern France. Other 
enthusiasts noted signals on v.h.f./ u.h.f. from the Low 
Countries and West Germany (see our correspondents' 
letters). My own log for the period is as follows : 

I /8/71 USSR Rl, R2; TVP (Poland) R2; MT (Hungary) 
Rl, R2; CT (Czechoslovakia) Rl and R2 twice; 
JRT (Yugoslavia) E3, E4; RAI (Italy) 1A, IB; 
ORF (Austria) E2a, E4; TVE (Spain) E3; BRT 
(Belgium) E2 via trops.; also unidentified signals. 
2/8/71 NRK (Norway) E2, E3; SR (Sweden) E2; RAI 

IA; plus unidentified signals. 
3/8/71 USSR Rl; JRT E4; ORTF (France) F2. 
4/8/71 CT Rl; USSR Rl, R2; ORF E2a; also unidenti- 
fied signals. 
7/8/71 Rumania R2; TVP Rl, R2; USSR Rl, R2; ORF 
E2a; JRT E3, E4; SR E4; NRK E2, E3; West 
Germany E3; RAI IA, IB; TVE E2, E3, E4. 
8/8/71 USSR Rl, R2; TVP Rl, R2; CT Rl; MT Rl; 
JRT E3; RAI IA. 

9-10/8/ 71 BRT E2 trops. 

12/8/71 USSR Rl; TVE E2, E3; West Germany E4. 

13/8/71 DFF (East Germany) E4. 

14/8/71 USSR Rl, R2; TVP Rl, R2; NRK E2, E3; SR 
E2; DFF E4. 

15/8/71 TVPR1. 

16/8/71 Various Northern French trop. signals. 

17/8/71 Various trops. including NOS (Holland) E4; 
BRT E2. 

20/8/71 DFFE4. 

21/8/71 BRT E2. 

22/8/71 West Germany E2; BRT E2. 

23-24/8/71 BR F E2. 

26/8/71 NRKE2;SRE3. 

27/8/71 USSR Rl; TVP Rl, R2 (extremely strong Rl 
signals); SR E2. E3. 

28/8/71 SR E2, E3; NRK E3, E4; TVP Rl; RAI IB. 




TELEVISION 

ROGER BUNNEY 



29/8/71 
30/8/71 



DFF E4; TVP Rl; BRT E2 (trops). 
DFF E4; BRT E2 (trops). 






It is interesting to note that the openings towards the 
end of the month seemed to occur during the evenings, 
in each case favouring the East European and Scan- 
dinavian directions. An additional opening was noted by 
Maurice Opie (Ringwood) on August 25th at Midday with 
various East European stations. 

Too late for the last column was the appearance on 
July 31st and August 1st of the Czechoslovak electronic 
test pattern on ch.R2. This is similar to the CS U 01 type 
but with a different identification consisting of three 
letters the first two of which were LT. On both occasions 
it was observed floating with the usual Chechoslovakian 
test card whilst the companion pattern was on ch.Rl 
again floating with the test card. A test card of a different 
type was noted by Maurice Opie on August 12th. At 
1605 he observed on ch.Rl a slow fading test card which 
lasted for four minutes before eventually disappearing 
completely. It consisted of a dark square standing on end 
within which was a lighter coloured circle containing 
what appeared to be three letter:. Surrounding the square 
were various lines and light coloured corner circles. The 
overall background was greyish. The characteristic type 
of reception suggests a long propagation path, either 
single or double hop, and we are wondering if indeed 
this may be Bulgaria. At present we are awaiting the 
test card information from Bulgaria for our Data Panel 
series so with any luck we will shortly know the answer 
to this mystery reception. Has anyone seen anything 
like it? 

Another mvstery from Hugh Cocker of Mayfield. 
Sussex. He has reported seeing the USSR 0249 card with 
alternative identifications (other than reported in Septem- 
ber's column). Apparently he has noted the card carry- 
ing the identification TA5 0249 or possibly TAS 0249. I 
have personally seen only the CCCP variation to this 
card but will be keeping a much closer watch in future! 



News Items 

Finland: We understand from a contact that YLE are not 
too happy with the performance of the Tampere ch.E2 







ORF Austria identification slide. 



Ping-pong from Peking Television. 






37 



DATA PAKEL 4— 2nd series 





Standard Pattern: Colour Blackboard 



Malta Television Service Test Card 





Gibraltar Television Identification Slide 
Standard Test Card G is used 



Cyprus Broadcasting Corporation Identification 
Slide, Standard Test Card G is used 



Photographs courtesy P. D. pan der Kramer, Gibraltar Broadcasting Ltd., The Malta Television Service Ltd., 
Cyprus Broadcasting Corporation. 



(TV2) transmitter and that it is likely to be replaced with 
a u.hi. transmitter in the future. . This is extremely bad 
news: Tampere is possibly the most frequently received 
DX-TV transmitter— certainly in the UK — and if it closes 
Finland is going to be a most difficult country to receive. 
The other Band I transmitters there are more distant and 
are rarely received. If this closure goes through Finland 
is going to become as rare as Bulgaria — at least in the 
Southern part of the UK. 

Other news from Finland : Sippola ch.E49 is now on 
test 0700-1400, power unknown; Lahti ch.E40 will be 
opened during the first half of 1972 with either 600kW 
or lOOOkW e.r.p. 

USA: Our friend Ferdinand Dombrowski of the WTFDA 
Milwaukee has advised us that the World's most power- 
ful u.h.f. transmitter is now in operation: WCCB-TV on 
ch.A18 has increased its power to a full 5MW (5000k W) 
e.r.p. The transmitter is situated at Charlotte, North 
Carolina and relays the ABC Network. 
Austria: We understand that ORF are to drop the Tele- 
funken card and use the electronic card on both v.h.f. and 
u.h.f. Fortunately an identification — either ORF 1 or 
ORF 2 — will be carried. P. D. van der Kramer has 
kindly sent a photograph showing an ORF identification 
slide. This impressive caption is shown when the 
National Anthem is played— 1 assume at the start and 
close of transmissions, 
Belgium: We have referred in previous columns to this 



country using the ORF type electronic card. The only 
transmitter to use this is Wavre, on u.h.f. only — chs. E25, 
E28. 

Sunspots: Predicted smoothed monthly counts for the next 
six months : August 62, September 60, October 58, Novem- 
ber 56, December 54, January 52. Courtesy Swiss Federal 
Observatory, Zurich. 

Reception During the Winter Months 

With the approach of Winter reception tends to fall to 
a rather low level, certainly compared to Summer condi- 
tions. It is still possible however to receive signals over 
similar distances to those of Sporadic E during these 
quiet periods — by means of meteor shower ionisation. 
The Earth is bombarded throughout the 24- hour period 
by particles — often no larger than grains of sand — from 
space. These meteorites burn up due to friction when 
they enter the various layers that surround the Earth 
and can cause intense ionisation at E-layer heights. Such 
ionisation is localised and of short duration but it is 
nevertheless possible to obtain signal reflection over dis- 
tances up to 1400 miles. Fast-travelling particles burn 
up sooner and thus higher, increasing the possible skip 
length; slow-travelling particles burn up lower down to 
give a shorter skip path. 

With this type of signal the receiving equipment must 

— continued on page 39 






38 




G.R.WILDING 



Weak Line Hold 

"Intermittent lines across the picture" was the 
complaint with a Philips Model G19T210 and in- 
spection showed that line lock on 405 could only be 
obtained with the line hold control fully clockwise. 
625 was unobtainable in the district. In these 
Philips models there is an additional preset line 
hold control mounted on the chassis. The correct 
setting-up drill is first to switch to 625, lock the pic- 
ture with the main (exterior) control, then switch to 
405 and lock by adjusting the preset. We found that 
this preset control was also in an extreme position 
so it appeared that either one or both of the ECC82 
valves in the line generator/ a.f.c. circuit (Fig. 1) 
were of low emission or that a component had 
changed value. 

Changing both valves scarcely affected the lock- 
ing position so we commenced voltage checking. All 
voltages were about normal except at V2004B 
anode which should have been 42V on 405 but was 
only slightly over 30V. This voltage reduction could 
have been caused by either an increase in value of 
the anode feed resistor or a reduction in grid bias 
causing excessive anode current: there was no 
capacitor to chassis which might have developed 
a leak. The 56kfi anode resistor proved to be in 
order but the 470kH grid resistor — returned to the 
h.t. line instead of to chassis — was well under 400kH 
and therefore failed to sufficiently offset the negative 
self-bias developed by the valve. Replacing this 



resistor restored a midway locking position to the 
line hold control. 

On subsequent test we found that if the contrast 
was advanced too far almost every other line would 
be intermittently displaced to the right by about a 
quarter of an inch, resulting in the appearance of 
two pictures slightly horizontally displaced. Our 
first suspicion was that excessive contrast was im- 
pairing the action of the line sync amplifier and 
phase comparator valve V2003, However we then 
found that this unusual effect could also be obtained 
by advancing the brilliance control too far while if 
it was turned to its extreme position the effect dis- 
appeared leaving a normal if very milky picture. 
The fact that this fault could be produced by two 
different actions completely changed the situation 
for the only common effects produced by increasing 
the contrast or brilliance were (a) the mean c.r.t. 
grid -cathode voltage would be reduced and (b) the 
e.h.t. current demand would rise. 

As in all flywheel sync circuits a reference pulse 
feed from the line output stage is fed to the dis- 
criminator — or comparator in this Philips model — 
which develops the d.c. control potential used to 
control the line generator. It seemed likely there- 
fore that the extra e.h.t. demand was affecting this 
pulse. As the DY87 valve was most directly in- 
volved we tried changing this first, but with no im- 
provement. On replacing the PL500 line output 
valve however the effect completely vanished. 

It is worth mentioning that in many colour 
receivers the "sensor" of the e.h.t. is the voltage 
developed across a low- value resistor in the cathode 
lead of the line output pentode. When due to in- 
creased output this voltage rises above a predeterm- 
ined level a beam limiting arrangement biases back 
a stage in the luminance channel. 

While on the subject of these Philips receivers it 
is worth noting that a not uncommon cause of in- 
sufficient width is an increase in value of one or 
both of the two 8-2Mfi resistors in the v.d.r. width 
stabilising circuit. Normally lack of width when the 
h.t. rail voltage, fine output valve screen voltage and 
line oscillator anode voltage are normal tends to 
make one suspect the boost reservoir capacitor or 
shorted turns on the line output transformer. But in 
these models as in the previous Style 70 series first 
check these two resistors (R427 and R457, see Fig. 1, 
May 1971, page 313) between the boost h.t. rail and 
the stabilising v.d.r. Similarly in other makes with 




Reference pulses from 
line output transformer 

Fig. 1: The fine osci/tator/a.f.c, circuit used in the Phi/ips 210 chassis. 






39 



v.d.r. width stabilisation always check the feed 
resistors from the boost rail when the width is not 
up to standard and follow makers' instructions when 
resetting the width control as this directly affects the 
boost rail potential. 

Delayed Colour 

Although in a BRC colour model fitted with the 
2000 chassis a black-and-white picture would always 
appear after the normal tube warm-up time it would 
sometimes be an extra ten minutes or more before 
colour developed. The owner found that a delayed 
start could usually be cut short by rapidly changing 
channels. 

On test it was found that when colour failed to 
appear "ditching" the colour-killer by connecting a 
100k ft resistor between the positive l.t. rail and the 
base of the first chrominance amplifier VT13 failed to 
produce either the colour signal or confetti. This 
made it all the more likely that the reference oscil- 
lator was at fault, usually needing a slight electrical 
impulse to start it operating. 

This suspicion was fully borne out when making 
voltage checks on this stage (VT4) and the d.c. 
amplifier (VT3) preceding it as test-prod application 
to most circuit points would instigate the reference 



signal. As no dry-joints were apparent we first tried 
a new oscillator transistor (BF115). This completely 
cured the warm-up delay. 

No Vision or Sound 

Called to deal with a no signal complaint in a modern 
single-standard KB model fitted with the VC200 
chassis we found no raster either, indicating a line 
timebase fault. Sure enough the line output pentode 
was labouring, indicating lack of drive, and on replac- 
ing the PCF802 line oscillator valve normal results 
were restored. Why no sound? It is worth noting that 
in this and several other single-standard chassis (e.g. 
GEC/Sobell and the Bush /Murphy TV181S/V2016S 
series) the l.t. supply for the transistor stages is 
obtained from .the line output stage — from a diode 
which rectifies the scan waveform fed to it from a 
low-voltage winding on the line output transformer. 
Failure of the line timebase will therefore remove the 
sound and vision signals as well. There have been 
reports of fine oscillator failure being caused by 
defective capacitors in the PCF802 circuit, so these 
(CI 24-7) might need checking. As in the Philips 210 
chassis lack of width can be caused by a changed 
value resistor in the width stabilisation circuit, in this 
case R159 (10MA). 



LONG-DISTANCE TELEVISION 

— continued from page 37 

have high gain and be able to synchronise at once since 
only short bursts of signal are experienced with a meteor 
shower (abbreviated to MS). One needs of course to be 
able to tune exactiy to the required channel. Signals 
throughout Band I are propagated by this means and 
the best time for random meteorites is the early morning. 
Signal duration can be anything from half a second to 
five seconds plus though the usual burst rarely approaches 
five seconds. If Band I is very active it may at times be 
worthwhile to check the lower end of Band III : MS at 
these frequencies does happen. 

At times the Earth encounters the more active regular 
Meteor Showers which can produce spectacular recep- 
tion. Forthcoming we can expect the Leonids November 
15th-17th, the Geminids December 10th- 14th and the 
Ursids December 22nd-23rd. Random reflections can 
occur at any time on any day. The distances usually 
experienced with this type of reception are between 700- 
900 miles but with the more active showers reception can 
become much more consistent and stronger with greater 
distances. We will be listing all the main meteor shower 
dates for 1972 next month. 

From our Correspondents .... 

Two interesting letters have come from a father and 
son DX-ing team : J. E. May (Orpington) and R, J. May 
(Ashford, Kent) have sent in details of their individual 
and combined reception. Both have experienced the pro- 
longed and excellent conditions this season, including the 
Czechoslovakian CS U 01 pattern. Most other countries 
in Europe have also been received in their respective 
parts of Kent. 

Frank Smales (Pontefract) has forwarded a long letter 
detailing the signals in Yorkshire for this season. Frank 
certainly seems to have been busy and asks our assistance 
with the identification of a mystery signal. On May 24th 
he noted on ch.E3 a clock at one hour ahead of our time 
— 1625 BST. The clock had a second sweep hand and there 
was Arabic writing or script beneath the clock. He won- 
ders if this might be Jordan as they are plus one hour 
BST (plus two hours GMT) at this time. It certainly 
sounds as if Frank may have received one of the exotics : 
a fine achievement if he has! We await further con- 



firmation ; did any one else note this signal at the above 
times? 

Our French TV expert John Penruddocke (Salisbury) 
has been logging ORTF on various frequencies and 
advises us that ORTF-1 has been noted on 625-line tests 
on Wednesday mornings — in addition to Tuesdays as 
previously noted. On some mornings ORTF has been 
on test before 0800 BST and thanks to the improved 
tropospheric conditions John has been able to take full 
advantage of the many French transmitters available to 
him at his hill-top home. 

Ian Beckett (Buckingham) writes to advise of his colour 
DX reception at the end of the month when the tropo- 
spherics improved to present him with two new West 
German u.h.f, transmitters and a number of old 
favourites. 

An extremely interesting letter has arrived from an 
experienced TV-DX enthusiast in Australia. George 
Peterson of Ayr, Queensland, may be remembered by 
established DX enthusiasts for his F2 /Trans Equatorial 
(TE) reception at the time of the last sunspot maximum. 
He has sent a large number of photographs which we 
are still looking through. One we selected at random 
shows very recent reception of China via TE. This was 
taken during the 1971 Ping-Pong matches in Peking and 
we have pleasure in including the photograph this month 
to show the characteristic mutiple-image effect of TE and 
also because the event was important in its own right — 
the photograph is possibly unique. The signal was re- 
ceived on ch.Rl. A number of Chinese transmitters 
operate on this channel but we are not too sure from 
which location the signal originated. As a rough guide 
the nearest transmitter listed on this channel is Nanking. 
4,750 miles ! 

Doto Panels 

With the colour blockboard we complete the series of 
standard patterns and are now going on to the patterns 
used by individual countries. Should other patterns which 
are commonly used come to hand in the future these 
will be included as standard patterns. We shall not be 
including transmitter details with the data panels as the 
number of transmitters now in operation is so consider- 
able. Accurate transmitter lists are available from the 
EBU, etc. 



40 



TU TE5T 



auihT 




E.M.BRISTOL 



BIB TAPE-RECORDER 
MAINTENANCE KIT 

The Bib tape-recorder maintenance kit is manufac- 
tured by Multicore Solders Ltd. for the purpose of 
keeping all parts of the tape path through the recorder 
clean and free from the oxide deposits which build up 
on heads, guides and pinch wheels. These can cause 
wow and flutter and on the heads give rise to loss of 
high frequencies and incomplete erasure. 

The Kit 

Housed in a blue plastic wallet, the kit comprises 
a bottle of Bib instrument cleaner, two blue tape-head 
applicator tools and two white tape-head polisher 
tools, ten polisher sticks, one double-ended brush, a 
packet of cleaning tissues and an instruction leaflet. 
Retail cost of the outfit is 4lp plus 8p p.t. 

For larger use and workshops there is a Professional 
maintenance kit which consists of two bottles of 
cleaner, 24 blue applicator tools and 24 white polishers, 
100 polishing sticks, two double-ended brushes and 
six packets of tissues. There are also four copies of 
the instruction leaflet. This kit retails at £2-80 plus 
56p p.t. 

Applicator and Polishing Tools 

The applicator and polishing tools consist of plastic 
material about 4£in. long and bent at one end to an 
angle of 150° where they are fitted with rectangular 
felt cleaning pads. There is no difference in the two 
types except for colour. This enables one to be kept 
clean for polishing while the other does the dirty 
work. The width of the pads is cut exactly to the size 
of the tape thus enabling them to fit into the tape- 
guides without missing any part of the surface — 
■ — especially the corners — where deposits can build up, 
A snag with these tools is their thickness : the handle 
is £in. thick and the felt pad is |in. There are a 
number of recorders where it is impossible to get the 
tool anywhere near the heads while with some of 
those that are reachable it is necessary to remove the 
pressure pad to do so. 

Polishing Sticks 

The polisher sticks are intended for use where this 
difficulty is encountered. These are short sticks with 
a pad of cotton wool encasing each end. One end is 



used with the cleaning fluid for cleaning and the other 
for polishing. They can only be used once as the pad 
comes away from the stick when soaked in the fluid. 

Use 

Really though the tool is the more convenient if 
only it can reach the head. While there will always be 
some awkward recorders that defy any cleaning tool, 
the usefulness of the tools in this kit could have been 
extended by a reduction in size. Very little pressure 
is needed in cleaning — the fluid does the work of dis- 
solving the deposits — so the part of the tool supporting 
the cleaning pad need be only thin. The pad itself 
could also be less thick and the total reduction in 
thickness of tool and pad would have enabled it to be 
used with many more recorders. 




When dirty the pads can be cleaned with a little of 
the fluid and the cleaning tissues supplied. It is as 
well not to let them get too dirty in between cleans. 

Cleaning Fluid 

A generous supply of fluid is given. Methylated 
spirit is generally used for this purpose but the makers 
claim that meths can have a deleterious effect on the 
rubber pinch wheel. The cleaning fluid does not have 
this effect and so can be used with confidence on rub- 
ber parts. Some badly caked heads however failed to 
"come clean" and recourse had to be made to the 
meths bottle. 

Double-ended Brush 

The double-ended brush is a useful item : it is 
constructed of twisted wire, one end being a conven- 
tional circular brush and the other a spiral-type pipe- 
cleaner pattern. Both enable fluff to be cleaned out of 
the nooks and crannies around the heads and guides. 
Being made of wire the brush can be bent to any angle 
needed to reach into difficult positions. 

Conclusion 

All in all this is a useful and inexpensive kit which 
should prove its worth to all concerned with the use 
and maintenance of audio and videotape recorders. 
NEXT: KLIK RIVETER 







41 



YOUR 

PROBLEMS 




PYE CT72 

The picture detail is OK on black-and-white but 
the colours tend to run into horizontal bands across 
the screen. The fault can be cleared temporarily by 
changing channel several times. Also there are on 
some occasions intermittent changes in colour inten- 
sity. — G. Ryle (Leicester). 

The reference oscillator on the decoder panel is 
intermittently off lock. Adjust RV10 then set a.p.c. 
bias control at the back of the decoder panel for op- 
timum results, which should correspond to 5V at TP5. 

PHILIPS 1768U 

There is an oscillation on the sound — it is not 
always present — which can sometimes be stopped by 
tapping the cabinet sharply.-^R. Quomley (Chester). 

The bias for the two sound i.f. amplifier stages is 
derived from the cathode circuit of the PCL83 audio 
valve. You should thus check the 100/xF electrolytic 
in the PCL83 audio valve cathode circuit (wired from 
pin 7 to chassis). 

FERRANTI 71084 

Due to asynchronous working the picture rolls 
erratically on n.h.f. every 30 seconds or so. It also 
causes line tearing approximately a third of the way 
down the screen, especially on long camera shots. 
Extra main smoothing has been added and the 30PL13 
field timebase valve replaced without making much 
difference. — A. F. Fellows (Dorking). 

We suggest you check the PCL84 video amplifier 
screen decoupling capacitor C55 (2,*dF) to pin 9. Check 
the PCL84 itself as well and the 30FL1 sync separator 
screen decoupling capacitor CI 22 (2^F) to pin 7. 

PYE V700A 

There is a wavy "bulge" on the left-hand side of 
the picture on this set. Sometimes this moves slowly 
from top to bottom and sometimes from bottom to 
top. I understand this is due to faulty smoothing. — 
G. Freeman (Axminster). 

You are correct in suspecting the smoothing and a 
good electrolytic bridged across each smoothing 
capacitor in turn will show up the defective one. 
Suspect also heater-cathode leakage in the line output 
valve. 



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MURPHY V470 

After the set has been on for about an hour there 
is motor-boating which drowns the normal audio. 
The picture is good at all times: could you explain the 
sound trouble? — C. Graper (Blackpool). 

The problem is that the sound i.f. amplifier V8 
(6F23) is going unstable. Check especially the screen 
decoupler C49 (000 1 /xF). This can often be stabilised 
by being moved slightly. 

PYE CT78 

There are vertical striatums on the left-hand side 
of the screen. These were accompanied once by a 
series of broad, faint vertical coloured bars across 
the whole screen. — G. Dodson (Goole). 

It seems that the flyback blanking transistor in the 
cathode circuit of the luminance output valve V6 on 
the colour-difference amplifier panel is faulty. This 
is VT28, type BC147. 

ULTRA 1760B 

When the volume is increased above a certain level 
the picture becomes ragged indicating loss of the 
sync. The audio circuits appear to be all right and 
the trouble does not seem to be acoustically induced 
because an external loudspeaker has been tried with- 
out the fault being cleared. — F, Best (Stockton). 

The effect you describe seems to indicate coupling 
via the h.t. line and we suggest therefore that you 
check the main electrolytics CB%\ C99 (100+200/*F) 
and the two sub-h.t. feed decouplers C76 in the audio 
section and C50 in the video and vision i.f. h.t. feed 
(8 + 16/xF). 

PYE 11 U 

There is foldover from the bottom with shrinking 
from the top. Eventually only a narrow band is left 
across the centre of the screen: this change coincides 
with the warm up of the set. I have changed the 
relevant valves and the voltages appear to be correct. 
Might the output transformer be at fault? — J. Jepsom 
(Hanwell). 

A faulty output transformer is unlikely to be the 
cause of this trouble. Suspect the cathode components 
of the output valve, R77 (390fi) and C74 (200,«F) and 
the feed resistor to this stage R75 (270fi). 



42 



GEC 2022 

The line hold needs constant adjustment and it is 
sometimes possible to achieve line lock only by 
adjusting L65. The line timebase valves have been re- 
newed but the fault remains. — H. Short (Sunderland). 

We suggest you replace the flywheel line sync dis- 
criminator diodes MR1 and MR2. If the diodes are 
not at fault — they must of course be a matched pair — 
check for dry-joints and poor contacts on the time- 
base panel. 

PYE CTM17T 

There are two faults in this 17in. set. First the sound 
went. It was restored by fitting a new PCL83 but 
subsequently it began to fade again. Secondly there 
is a gap about 2in. wide at the top and bottom of the 
screen. The field timebase valves have been replaced 
without effecting a cure.— G. Upton (Brighton). 

A common fault producing the two symptoms you 
are experiencing is inadequate smoothing. You can 
check this by bridging a good electrolytic across each 
smoother in turn. Alternatively suspect a low h.t. 
rectifier. 



FERGUSON 3623 

The first fault to occur was loss of horizontal and 
vertical hold on both systems; there are dark diagonal 
bands across the screen which rotate first in one direc- 
tion and then the other. Secondly there is Complete 
loss of sound and vision on u.h.f. although the raster 
is OK: both tuner valves have been replaced. — G. 
Orford (West Bromwich). 

First check the PFL200 and its operating condi- 
tions, also the line sync diode W4. The absence of 
u.h.f. signals is probably due to the switch on the 
v.h.f. 'tuner being inoperative owing to the bowden 
cable being out of position : note the effect of operat- 
ing this by hand. 



BUSH TV96 

This set has developed a severe field fault. After 
the set has been on for a time varying between half 
to two hours a very fast field spin develops, so fast 
in fact that the picture appears as if there was a ghost 
signal superimposed. The field hold functions over the 
whole control range. AH valves likely to cause the 
trouble have been replaced without success and also 
the coupling capacitor to the grid of the valve where 
the hold control is connected. — G. Taverner (Rhyle). 

We suggest you change CI 08 (0-05^F) the field 
multivibrator cathode decoupler and R12l (620kO) 
which is in series with the field hold control. 

GEC 2019 

The problem with this set is no sound or vision on 
y.h.f. although the raster is OK. Reception on u.h.f. 
is normal. The valves in the v.h.f. tuner have been re- 
placed without effecting a cure.— D. Bridle (Cheadle). 

If the voltage supplies to the v.h.f. tuner are pre- 
sent it would appear that one (or more) of the re- 
sistors in the tuner have changed value. Check in 
particular the 5*6kn and 6-8kft resistors in the oscilla- 
tor anode circuit. To gain access it is necessary to 
dismantle the tuner: these resistors will be found at 
the top under a strip of tape. 



PHILIPS 511 

The trouble is poor focus at the centre of the screen 
»nd defocusing on bright parts of the picture — the 
Scanning lines are sharply defined at the side edges. 
The focus control is set at one end of its travel (the 
lower-voltage end). The e.h.t. shunt bias adjustment 
has been correctly sec in accordance with the 
manual. The only other fault that has been ex- 
perienced on this set is the line output valve screen 
feed resistor going open-circuit: this was replaced 
using a component with 5\V rating. — L. Charles- 
worth (Harlow). 

As the focus control is set hard to one end we sug- 
gest you check the values of the high-value resistors 
in series with it on the low-voltage side (R5046-5050). 
Also check the EY51 focus rectifier. 



RGD 624 

V.H.F. programmes appear only with the contrast 
control set to one extremity of its travel whilst on 
changing to u.h.f. the contrast control has to be 
turned to its other extremity in order to obtain a 
picture. There is always a raster present. — T. Wimple 
(Stockton), 

The problem is associated with the pulsed a.g.c. 
amplifier stage V3B, the triode section of the video 
PCL84. First try opening the panel and adjusting the 
preset contrast control 117: this operates on v.h.f. only 
and could solve your problem. Otherwise you will 
have to check the various resistors associated with 
the triode section of the PCL84, in particular 127 
and 128 which feed the grid, the contrast control 
124A and its series resistor 125, and the 10MH resis- 
tor 132. 



COSSOR CT1972A 

There is no picture or raster. A low line whistle can 
be heard but the DY86 does not light up. If the PY800 
is removed the whistle is harsh, the DY86 lights up 
and a small picture appears in the centre of the 
screen. When the PY800 top cap is removed the glass 
of the DY86 gives a blue discharge to a screwdriver 
blade. The DY86 and its heater winding have been 
replaced, also the I'YSOO and PL36 which is over- 
heating. — K. Johnson (Wolverhampton). 

The boost reservoir capacitor is almost certainly 
short-circuit. In this chassis it consists of two 0-05/xF 
capacitors connected in parallel to form <M/*F. They 
are mounted together under the PCL85. You could 
replace both with a single 0-1 ,uF capacitor rated at 
lkV. 



BUSH T67 

The trouble is fading after the set has been on for a 
little time. Sometimes the fading disappears and the 
picture becomes almost perfect, then the fading 
starts again — it is mostly apparent at the bottom of the 
screen. The main smoothing electrolytic has been 
replaced. — J. Corvin (Barking), 

Your description suggests that the PCF80 video 
amplifier valve on the left side has heater-cathode 
leakage. This would produce a faded picture, particu- 
larly at the bottom. Also check the EB91 in the vision 
section by swopping with the other EB91: hum on 
sound will be the result if the vision EB9I is respon- 
sible for the trouble, the vision then being clear. 



43 



PYE CT72 

Sometimes after about four hours' operation the 
following colour fault will appear: the yellow and 
blue content fade and the whole screen appears 
darkish green. On operating the colour control flesh 
colours appear pale to bright pink. The condition 
lasts for ten minutes to a quarter of an hour after 
which the picture slowly returns to normal. Switching 
off the blue does not give the same effect as the 
fault.— S. Graham (Derby). 

Your B— Y signal is intermittent. Check around 
the small blue link beside the delay line on the decoder 
panel and also the colour-difference output stage V9 
(PCL84) on the colour-difference amplifier panel. 



PHILIPS 19TG156A 

After about half an hour the sound disappears and 
the picture bows in at each side: when the volume 
control is turned down the sound and picture return 
to normal. — G. Braithwait (Southport). 

The PCL83 sound output valve could be respon- 
sible for the conditions you describe. Check this by 
replacement, examine the drop-off bias resistor R223 
and check the 250// F electrolytic CI 10 which smooths 
the HT1 line from which the stage is fed. If there is 
a positive voltage at the hot end of the volume con- 
trol replace the coupling capacitor C228 from pin 1 
of the PCL83. 



TEST X^ 



MARCONIPHONE 4705 

On turning up the contrast the verticals are 
impaired, pulling to the left. I have readjusted to the 
maker's instructions without improving matters. The 
set works all right when the contrast control setting 
is below normal. — F. Bilton (Stoke). 

The fault sounds like an a.g.c. one. If you have 
set the set a.g.c. preset R125 correctly you should 
have a difference of 4-9 V across the luminance delay 
line output pins using method 2 detailed in the 
manual. Check the voltages around the a.g.c. ampli- 
fier VT106 and the associated components — particu- 
larly the electrolytic CI 34. If this does not reveal the 
source of the trouble make voltage checks around the 
post luminance delay line amplifier VT201 and then 
the vision i.f. stages VT101-VT104 — in that order. 
These sets are rather prone to this fault however 
when the contrast is at maximum. Try adjusting the 
local /distant control R5 (r.f. gain). 



107 



Each month we provide an interesting case of 
television servicing to exercise your ingenuity. 
These are not trick questions but are based on 
actual practical faults. 

■Jl A few weeks after the installation of an ITT 
5 colour receiver the owner complained of the pic- 
ture disappearing after about 30 minutes running, 
leaving a bright, horizontal line on the screen, and 
that the trouble could be cleared by switching the set 
off for a few minutes, invariably this action resulted 
in the set working normally for the rest of the even- 
ing. The technician dispatched to correct the fault 
found on arrival that the set was working normally. 
After a couple of cups of tea however and with the set 
now quite warm the symptom described suddenly 
appeared. 

After quickly reducing the setting of the brightness 
control to avoid damaging the screen the technician 
turned back the volume, asked for complete quiet and 
then put his ear close to the rear of the set while 
adjusting the vertical hold control. Mumbling appro- 
priately, the technician then switched off, removed 
the back cover while his soldering iron was running 



QUERIES COUPON 

This coupon is available until November 22, 

1971, and must accompany ail Queries sent 

in accordance with the notice on page 41. 

Don't forget the 10p postal order! 



i 



TELEVISION NOVEMBER 1971 



I 
I 



up to temperature and within 15 minutes, without 
making any replacement, had remedied the fault. The 
remedy was proved to be permanent by a delighted 
customer ringing a week later and extolling the singu- 
lar genius of the field technician! 

How did this technician discover so quickly the 
source of the fault without making any measurements 
and then clear it with a soldering iron alone? See 
next month's Television for the solution and for a 
further item in the Test Case series. 

SOLUTION TO TEST CASE 106 
Page 570 (last month) 

While it is well known that a fault in the Y delay 
line can horizontally displace the luminance from the 
colour, it is not so well known that in receivers with 
primary-colour drive in particular change in the 
bandwidth characteristics of one primary-colour 
channel with respect to those of the others can result 
in a similar displacement with respect to the appro- 
priate colour. 

Emitter compensation is often used in each primary- 
colour amplifier and in the case in question it was 
found that a capacitor in the emitter circuit of the 
blue channel had gone op en -circuit. This affects the 
gain of the channel and also widens the bandwidth 
because of the negative current feedback introduced. 
Thus the blue signal arrived at the blue gun a small 
fraction of a second before the other two signals 
arrived at their guns. Replacing the faulty component 
cleared the fault but the technician then found it 
necessary to readjust the primary-colour channel gains 
for the best display. 



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AW53-80 £7 50* 

AW53-88, 53-89 £8-25 

AW59-90, 59-91 £900 

C17LM,17PM, 17SM .. £6-50 

CME1201 , £12-50 

CME1402 £5-75 

CME1601 £10 50 

CME1602 £12 OQ 

CME1702, 1703 £6 75 

CME1705 £7-75 

CME1713/A44-120 .... £14 50 

CME1901 ,1903 £7 50 

CME1906 £12-50 

CME1908 £7-75 

CME2013 £12-50 

CME2101,2104 £8-25 

CME2301,2302, 2303 £9 00 

CME2305 £14-75 

CME2306 £13-50* 

CME2308 £9-95 

CME2413R £16-50 

CRM93, 124 £5 50* 

CRM141, CRM142 .... £5 50 
CRM171,CRM172 .... £6 50 
CRM211, CRM212 .... £7-50* 

MW36-24, 36-44 £5-50 

MW43-69 £6-75 

MW43-80 £6-75 

MW53-20, 53-80 £7 50 

TSD217,TSD282 £14 00t 

13BP4 (Crystal 13) . ... £14 00t 

190AB4 £9-25 

230DB4 £11 25 

t Rebuilt tubes also, 
at £700 plus bulb 
*These types are FULLY rebuilt. 

ALL TUBES ARE TESTED AND GUAR- 
ANTEED FOR A MINIMUM OP 
12 MONTHS 

ADD 7Bp FOR CARRIAGE AND 
INSURANCE 

COLOUR TUBES 
19 in. and 22 in. having slight 
marks or scratches at £35 each 

TELEVISION TUBE SHOP 

48 BATTERSEA BRIDGE ROAD, 
LONDON, S.W.1 1. 228 6859 

WE GIVE GREEN SHIELD 
STAMPS 



46 



SETS & COMPONENTS (continued) 



PHILIP H. BEARMAN 

A hading name in valves and Tubes I 

(Milliard, Thorn, Telefunken, etc.) 

NOTE: from 1.8.71 deduct 5% P/Tcx. 

NEW MOSTLY BVA VALVES! Huge range by post service well known to the 
trade. Brief list of television types herewith, full list S.A.E, All types ex stock I 



DY86/7 


43p 


PCF86 


63p 


PY82 


50p 


20 LI 


95p 


EB91 


25p 


PCF801// 


62p 


PY800/1 


50p 


20 P4 


£1-00 


ECC82 


42p 


PCF805 


87p 


R19 


85p 


30C15 


90p 


ECL80 


50p 


PCF808 


85p 


U25 


95p 


30C17 


95p 


EF80 


42p 


PCL82 


51p 


U26 


95p 


30F5 


95p 


EF85 


45p 


PCL83(S; 


60p 


U37 


75p 


30FL1 & 2 


65p 


EF183/4 


57 p 


PCL84 


60p 


U191 


90p 


30L15 


95p 


EH90 


55p 


PCL805/E 


5 66p 


U193 


48p 


30L17 


90p 


EY51 


60p 


PCL86 


66p 


U251 


95p 


30P12 


95p 


EY86/7 


43p 


PL36/8 


87p 


U301 


90p 


30PL1 


60p 


PC86&8 


75p 


PL81 


80p 


U801 


£1-25 


30P4MR 


£1-25 


PC97 


45p 


PL83 


85p 


6/30 L2 


90p 


30P19 


87 p 


PC900 


55p 


PL84 


65p 


6AT6 


55p 


30PL1 3 


£1-00 


PCC84 


50p 


PL500 


90p 


6BW7 


82p 


30PL14/5 


£1-10 


PCC89 


62p 


PL504 


90p 


6CD6G 


95p 


etc., etc. 




PCF80 


52p 


PY81 


50p 


6F23 


95p 


Trade prices 


POST FREE OVER £3-00. 2£p PER VALVE BELOW £3-00 





LATEST NEW BY100/127 type silicon rectifier 1 5p. 33D res 5p ! 
Large bulb Imported PCF80 32p! Note. Ask for separate component and 
Philips PCL805[85 57 p! tra ns istor I i sts , 

6 POTTERS ROAD, NEW BARNET, HERTS. 

(Adjacent to Post Office) 

Tel, 01-449/1934 & 449/1935 

(Robophone) 

(Suppliers to H.M. Govt, etc.) 



Special quantity terms, lists, 
s.a.e. GIRO 34.361.4006 



ELECTRONICS 
LOW NOISE HI-STABS 

i watt 5% all E24 values, 3 for 2p, plus p & p op 
for up to 60 resistors + 1 p f ot each additional 50 
Skeleto n Pn««U 01 watt Bp, 25 watt 7p. 
BjiF 64 v; 1BuJ= <0v, 6p. 10Ou.F 40v, Bp. 
640 nF 25 v, 18p. Polystyrenes Bp each. 
Silver Micas 7p each up to 220pf. C2SO, 
0*1 p,F 250v 3p. Food through Ceramic 
lOOOpf Bp. 

BC167 27p 



BC107 12p 

BC108 lip 

BF167 ZBp 

BF173 ZBp 

BF184 2Sp 

BF180 42p 



oa5o 7p 

OA95 7p 

2N1613 Z2p 

TAA700 tZ 

AC12S 17p 



BF194 17p 
BF19B 17p 
BF186 
(BF239)1Bp 
BF197 IBp 
BU105 E2-7S 
BZY88 range IBp each, 
T TL Decade Countei 7490 87 p 
Coax Socket Bp. Switch 2 polo 3 way ZBp 

FREE CATALOGUE P «V P 3p. 
P & P on atl orders other than Resistors 6p 
Dapt. "t", 58 Fort is Orean ltd., London, 
N10 3HN 



TOP 20 TV Valves, lOp; PL504, PL36. 
PY33. 15p, P&P 4p per valve, over 12 
valves post free. Guaranteed tested 
ex-equipment, individually boxed. 

Resistors and capacitors all values and 
sizes. Leading manufacturers compon- 
ents and hi-fi equipment, 10% or more 
off. 13A plugs, 12p. Mains fuses, 20p 
for 10. Tools, etc., P&P extra on all 
items. Trade enquiries welcomed, dis- 
count for quantity. S.A.E. for list. 
L & D Components Ltd., 71 Westbury 
Avenue, Wood Green, N.22. 
01-888 2701. 



120 NEW ASSORTED Capacitors, 
Electrolytic, Mica, etc., and Resistors, 
i/20W, 85p, Post Free. Whitsam Elec- 
trical, 33 Drayton Green Road, Lon- 
don, W.13. 



T.V. SPARES 



OIL FILLED MURPHY LOPT'a U26 type. 

Model number not known. £1-25 each plus 
21p p.p. 

BAIRD/FERGUSON V.H.F. TUNERS. 

Uses PC97 and 10C IS valves. Fits 620 to 650 
series models, complete with all coils, supplied 
leu valves, t£l 75 each plus 25 p p.p. 

BRC 960 l.F. PANELS. Complete and unused, 
less valves. Dual standard V.H.F./U.H.F. 
•105/625. Absolute bargain ac £2-50 plus 25 p 
P-P. 

FERGUSON/EKCO PLUG IN MAINS 
LEADS. Moulded two-pin connector type. 
6 for £1 -50 plus ISp p.p. 

LATE G.E.C.'SOBELL 625 405, etc Dual 
Standard 405/625 l.F. Panels, complete with 
switching for direct replacement in this 
popular Radio and Allied receiver. £1-73 plus 
23p p.p. 

TIMEBASE PANELS to fit Sobell 195, 282, 
283, 284, 285, 286, 287, 288 (and OS models), 
McMichael MT762, 763, 765, P40S, Complete 
and new for direct replacement, £1 75 each 
plus 15p p.p. 

V.H.F. ROTARY TUNER UNITS to fit 
McMichael, Sobell, G.E.C. New and unused, 
£1 '75 each plus 25p p.p. 

FERGUSON 800/850 series TIMEBASE 

PANELS, complete and unused in original 
packing, £2*25 each, pfus 25p p.p. 

SCAN COILS, 1 10° type will fit most makes, 
after modification. Originally manufactured 
for Pye but we have used them in BRC, Philips, 
etc. with good results. £1-50 plus 25 p p.p. 



WILLOW VALE 
ELECTRONICS LTD. 

4 & 5 The Broadway 
Hanwell, London, W.7 

Tel: 01 -567 2971 and 5400 
01-579 3582 



Terms cash with order or CO.D. 27 Jp extra 
S.A.E. all enquiries. Catalogue 2 Op 






SOUTHERN VALVE COMPANY 

44 Earls Court Road, London, W.8 



SPECIALISTS IN QUALITY VALVES FROM 
TOP MANUFACTURERS; WE DO NOT CLAIM 
THE LOWEST PRICE, BUT GENUINE VALUE! 

All new and boxed, some BVA. Send s.a.e. for iisl. 



DY87 

DY802 

E891 

ECC81 

ECC82 

ECL80 

EF80 

EF183 

EF184 

EH 90 

EY51 

EY86/7 



37p 
45p 
15p 
37p 
30p 
40p 
27p 
37p 
37p 
45p 
50p 
37p 



PC86&8 50p 
PC97 40p 

PCF80 
PCF86 
PCF801 
PCF802 
PCF805 
PCF808 
PCL82 
PCL83(s) 50p 
PCL84 37p 
PCL85 45p 



32p 
52p 
50p 
50p 
50p 
60p 
37p 



PCL805 45p 

PCL86 37p 

PL36 52p 

PL81 46p 

PL84 55p 

PL500/4 65p 

PY81 35p 



PY800 

PY801 

U25 

U26 

U191 



35p 

35p 
65p 
60p 
65p 



U193 

U251 

6/30L2 

6BVV7 

6CD6G 

6F23 

6F28 

20L1 

20P4 

30C1 5 

30F L1 & 

30L15 



35p 
62p 
60p 
60p 
90p 
75p 
48p 
85p 
90p 
70p 
2 75p 
75p 



30L17 75p 

30P1 2 70p 

30PL1 60p 

30P4MR 95p 

30P1 9 70p 

30PL13 75p 

30PL14 75p 
etc., etc. 

NOTE 

BYI DO/BY) 27 
equlv only 20p 
with resistor. 



POST FREE OVER £2, BELOW 2-Jp EACH. 
MAIL ORDER ONLY. 



47 



SETS & COMPONENTS 



AERIAL BOOSTERS £2-95 EACH 

We make four types of transistorized aerial 
pre-amplifiers. These take only seconds to 
install. 

1. L45 625 TELEVISION (U.H.F.). 

2. Lt2 405 TELEVISION (V.H.F.i. 
Please state channel numbers. 

3. LI I V.H.F. F.M. RADIO. 

4. LIO WIDEBAND RADIO. 

This covers M/W and S/W to 20 MHz. 

PRICE EACH 

L4S, LI 2 and LI I £2 95; LIO £1-95. 

S.A.E. FOR DETAILS 

MONEY BACK GUARANTEE 

P. & P. lOp ALL ORDERS 



VALVE BARGAINS 

Any I— I Op, 5— «p, 10— 70p. 

EB9I, EBF89, ECC82. EYB6, ECL80, EF80, 
EF8S, EF183, EFI84. PCC84, PCC89, PCCI89, 
PC97, PCF80, PCF86, PCF800. PCL82, PC97, 
PCL84, PCL85, PL36, PL8I, PL83, PY32, 
PY33, PY8I, PY82. PY800, PY80I, 30FLI, 
30 FS, 30LIS. 30C15, 6F23, 6-3QLZ. 
TESTED, WITH 3 MONTH GUARANTEE VALVES 
20p EACH 

BY100 TYPE RECTIFIERS with Surge- 
resistor on bracket, I2|p each, 
MAINS DROPPIRS 3 SECTIONS 33-33- 
33 OHMS 9p each. 



VELCO ELECTRONICS 

62c Bridge Street, Ramsbottom, Bury, Lanes. Tel. 3036 



R & R RADIO 

51 Burnley Road, Rawtenstall 

Rossendale, Lanes 

Tel.: Rossendale 3152 





TESTED VALVES— 






3 MONTHS' GUARANTEE 




EBFB0 


ISp 


PCCB4 ISp PY800 


I7jp 


ESF89 


I7ip 
ISp 


PCF80 ISp 


PY80I 


I71p 


ECCB2 


PCL82 20p 


UI5I 


22ip 


ECLB0 


ISp 


PL36 ISp 


30CIS 


ISp 


EFB0 


IDp 


PY33 ISp 


PCFB6 


ISp 


EF85 


ISp 


PY81 ITjp 


PCLBS 


25p 


EY86 


20 p 


PY82 ISp 


PCL8-4 


ISp 


Copper 


Lamin 


ate Board, for 


etching, 


p per 



sq.'n. Double sided I : p per sq.in. Any size cot, 
min. order SOp plus 10'. P. & P. 
Postage on Valves: one valve 4p, up to 6 2}p 
over 6 post paid. 



TOWERBY LTD 

For Line Outputs and Defector Coils 

We have the Country's largest stock of Manu- 
facturer's Original (or Authorised Replacement) 
Line Output Transformers for many "difficult" 
makes. Including Ambassador, Baird, Cossor, 
Decca, Dynatron. Ekco, Ferguson, G.E.C., 
H.M.V., K.B., Mastaradio, Peto-Scott, 
Philips, Regentona, RGD, Sobell, Ultra, 
etc. Also deflector coils output and oscillator 
transformers, inc. Alba, Bush, Murphy, 
Examples, L.O.P.T. Murphy 350 4 1 0/540 ,'659,' 
759, £7-35: Bush, TVflO. TV9S. TV96. £7 35: 
Conor 950, £387|: Ferguson 306/308, 
U»7r; Philips I768U L.O.P.T, assembly, 
£4 75; Ultra 1984-200:, «». 
Rewind most L.O.P.T., £4 SO. 

SPECIAL OFFER 
Ekco improved type for Models T22 1, 231, 310, 
all at £2 25: Ferranti I4T4 series inserts, CI 25, 
Phr I co 1019.1021, £2 62;. Terms: C.W.O. or 
C.O.D. (I7ip), post-packing 30p: 2 or more 
L.O.P.T. s post packing free. 
All enquiries answered but regret no lists 
available. Same day delivery on most types. 

TOWERBY LTD 

MAIL ORDER DIVISION OF T.C.S. LTD. 
70 STREATHAM HILL, LONDON, SW2 

Tel.: 01-674 2185. 



VALVES, VALVES, VALVES 

Any ten of your choice 72ip. post 5p. 

100 £5-50, post paid. 
EF8S. EF80, EB9I, EBF89, ECL80, 
EFI83, EY86, PCF80, PCC84, PL36, 
PY8I, PCL82. PCL83, PCCB9, PY33, 
PY82, PY800, PY80I, PY88. PCL84, 
30F5. 6BW7, PY80I. 

BOB'S, 

2 St, James Street, Rawtenitall 

Rossendale, Lanes. 

Mail order ONLY. 



TV's TV's TV's 

SPECIAL OFFER-LIMITED 
PERIOD ONLY 

19" Slim Thorn SUO TV's 13 channel. 

Good working order. Polished cabinets. 

Only £9-60 l'LUS ei'EO Carr, 

EX-RENTAL TV's (UNTESTED) 



Complete with 13 channel tuners. 


Good cabinets 


Carriage £1-50 extra. 




17" Semi Slim (90* Tube) . , 


.. t£50 


1 7"/21- Slim (110° Tube) . . 


., £4-50 


19" Slimline . . 


.. £6 50 


23' Slimline 


. 18-50 


19" BBC2 Sets 


.. 114-50 



PERFECT SPEAKERS EX T.V. 

Pm 3 ohm (minimum order two)- 5 In- rotmd. 8 in* by 
2 in. reeiangtiLar — 12ip each* Add Tip per speaker p F & p. 

VALVES EX EQUIPMENT 



EB91 


6p 


301,1 5 


lilp 


PL36 


22tP 


EBFS9 


12*P 


30P4 


12ip 


PL6I 


mt 


ECC82 


12tp 


FC97 


17tp 


PYB1 


IGp 


EC180 


7ip 


FCFS6 


nip 


PYBOO 


ISp 


EFB0 


12.P 


PCS I 


7|P 


PYS2 


7tP 


EF85 


12tP 


PCF80 


7iP 


PY33 


22iP 


EP1S3 


12ip 


FCCS9 


12SP 


0191 


17iP 


EF184 


12is 


i'*cr.t.s 


22tP 


6F23 


17H> 


ET86 


ir»p 


FCLB2 


17,p 


S0FL1 


2S*P 


30FL13 


30p 


FCL86 


17*P 


30P12 


20p 


630LZ 


lSlp 


FCL83 


DHP 


30F5 


lOp 


Add Zip 


pt-r vi.h 


e p. 4 p., o 

UHFTU 


rders On 

NERS 


er£l p. 


t p. free 



For Ferguson 850 900 chassis. Adaptable for KB, EKCO, 
T415, 1084 Chassis ££-50, p. £ p. SOp. 

SLOT METERS- SPECIAL 
OFFER 

Smiths Mk. 11 6d. Convertible to 5p, (Smiths Kit costs 
35p each £1 each inc. p. & pkg. or 10 for £5 lac. p, & pkg. 
Please write with 8AE tor quotations on but spares. 

TRADE 
DISPOSALS (Dept. T.S.) 

Thornbury Koundabout, Leeds Bd„ Bradford. 
Telephone 685670 



AERIALS 



BAKER and BAINES 

UHF Aerials. 82fi line. 10 element, £210. VI ele- 
ment, tS. 35, 18 element, £3-25, SI element, £3-75. 
.imilile S2 ..k-ni.;:,L, £8 00. 

BBC Aerials, 40S line. Dipole, £1 75, "X", £216, 
"H". I2-40. 

ITA Aerials. 405 line, 5 element, £1-99, 8 element, 
£8-70. 11 element., £3-80. Double arrays available 
of above. 

Conbined BBC ITA Aerials. 405 line. Dlpole plus 
five, £8-70. "H" plus the, £4-10, "X " plus Ave, £4-50, 
FM Band U Aerials. Dipule £118, two element, £3-00. 
Special loft Dipule and Hve BBC .'IT A with loft pole, 
£2-10. Chimney lashing*, 6", 80p. 12', II 16, IB', 
£2-35. 5' e 1- straight pole, Bin, V X 1" cranked 
pole 80p. Co-as. at Sp and Up per yard. UHF 
pre-amps £3-75 p. & p. 13p. POSTAGE PAID OK 
AERIAL3 INLAND ONLY, Accessories charged 
at cost. Please state channels on aerial orders or 
transmitter where you wish to get your picture from. 
11 Dale Crescent, Tupton. Chesterfield 



AERIALS 

UHF: Set Tops £2 10, Outside: 9 ele 
£125, 10 ele CI -90. II ele £2-50, 12 ele 
£2-55, IS ele £3 25, 20 eie £350. Multi- 
beam 46 and Supremes £5*50, 
All aerials supplied with clamps. 
ANTIGHOST: Troubleshooters,'' Log- 
beams £5. 

FMVHF: H £2 25, 3 ele £3 25, 4 ele 
£3 75. Sterio 6 ele £6. 
Motorized Units; Semi Auto £20, Auto 
£25. 

All Aerials by leading makers, 
ELECTRONICS, ACCESSORIES: 
Incl. Masts, Lashings, Plugs, Amps., 
Headphones, Meters, Stereo Cartridge 
Players, Cassettes. Tapes, etc, etc. 
CO AX I ALE: Standard 100 Mtrs. CA SO. 
Low Loss £7, or per Mtr. 
State channels lor all TV Aerials/Amps. 
FM state wide band or channelized. 
TERMS: CWO, COD, P & P 32|p. Send 
2^p stamps for lists. Callers Welcome. 

OVERSEAS customers welcome. Note 
New Zealand/Australia by sea, 7 weeks 
min. By Air quotations given. 

JEFFRIES SERVICES 

31 Hambrook St., Portsmouth. Tel, 28354 



Direct from the 
Manufacturers 

U.H J. AERIALS 



14 Element 18 Element 

£150 £175 

Ready assembled add 20p. 

allow 32'Ap. carriage and packiny. """ 

Please state which channels or group. 

TRADE SUPPLIED, SEND FOR LIST 

APEX AERIALS ( T.V. ) 

ALBAN WORKS, MARY ST., 
JOHNSTONE. RENFREWSHIRE 



THIS 



MONTH'S 
OFFERS 

TV COLOUR SET SCAN COIL plus 
convergence coil to scan 19" or 25" 
colour tubes. Brand new ., £3-9S 

UHF PRESS BUTTON TRAN- 
SISTOR TUNER less push button 
unit. Brand new £1-75 

VENNERTIMESWITCH.240v.mains 
operated. Will handle up to 10 amps. 
1 on/off in 24 hours. Ex-GPO £2'00 

TV MAINS SUPPRESSORS. Ideal 
to eliminate mains noise. Brand new. 
1 -5 amp . . £0-75 

MICRO SWITCHES. Complete with 
press button and mounting bracket. 5 
amp rating. As used by GPO. Brand 
new 10 for £1-10 

All prices include carriage and packing 

UK. Send SAE for full lists. 

M&B COMPONENTS- Leeds) LTD 

P.O. BOX No.1 25, 38 BRIDGE END. LEEDS. 

LSI 4EW Telephone: 0532-35649 



48 



PHILIP H. BEARMAN 

A leading name in values and tubes— trade and retail all welcome. 

TUBES GUARANTEED 2 YEARS, COLOUR 4 YEARS 

Large stocks by leading British and foreign manufacturers, mostly ex stock. 

1 1 in. TSD.282 £12-50. A28. 14W £10-50 Carriage 50p 

12 in. MW31.74 (CRM.124) £3-00. TSD.290/CME.1201 £9-80 Carriage 50p 
14 in. £4*75. 16in. Mono £7-50. Rimband £10-15 Carriage 50p 
17 in. £5-87. Rimband £11-55 (17 in. MW43-69 rebuilt only £5-25) Carriage 55p 

1 9 in. £6*87. Rimband £8-50. Twin panel £1 0-1 2. Carriage 60p 

20 in. £10-50 (A50.120WR— CME.2013). Carriage 60p 

21 in. £7-87. CRM.211, 212, AW53.80. Carnage 65p 

23 in. £9-50. Rimband £11-50. Twin panel £15-00 Carriage 65p 

24 in. £13-00. 25 in. £17-00. Both rimbands. Carriage 70p 
NOTE Tubes manufactured by Mutlard, Thorn and some foreign manufacturers. Carriage quoted excludes any sea 
Journey (50p extra). 

COLOUR! 4 YEARS GUARANTEE ON ALL TYPES 
19 in. A49.11 X and A.49.120X. £49-00 PLUS £1 CARRIAGE 

22 in. A.55.1 41 X and A.56.120X. £53-00 PLUS £1 CARRIAGE 

25 in. A.63.11X and A.63.200X. £57-00 PLUS £1 CARRIAGE 

We endeavour to maintain prices but all are subject to alteration without notice. 

6 POTTERS ROAD, NEW BARNET, HERTS. TEL: 01-449/1934 (Robophone) and 449/1935 




Learn at home... 
First Class Radio 
and TV Courses 



After brief, intensely interesting study — 
undertaken at home in your spare time — 
YOU can secure a recognised qualification 
or extend your knowledge of Radio and T.V 
Let us show you how. 
FREE GUIDE 

Free Guide contains 120 pages of 
information of the greatest importance to 
both the amateur and the man employed 
in the radio Industry. Chambers College 
provides first rate postal courses for Radio 
Amateurs* Exam., R.T.E.8. Servicing Cert., 
C & C. Telecoms., A.M.S.E. (Elec.). Guide 
also gives details of range of certificate 
courses in Radio/TV Servicing. Electronics 
and other branches of engineering. 



Write now for your copy of this valuable 
publication. It may well prove to be the 
turning point in your career. 
Founded 1885 Over 150,000 successes 

CHAMBERS COLLEGE 

(Ineorp. National Inst, of Engineering) 

jDept. 844V) Aldc-maiten Court. Reading. RG7 4PF 




U.H.F. TV AERIALS 

Suitable- lot Colour and Monochrome Reception 

A]l U.H.F. aerials 
now fitted with tilt- 
ing bracket and 4 
element reflector. 

LOFT MOTTNTDIO ARRAYS. 7 
element £2-25. 11 element £2 '73. 
14 element £3-25, 18 element £3-75. 
WALL MOUNTING o.'w WALL 
ABU AHD BRACKET. 7 eiement 
£3-23. 11 element £3-73. 14 ele- 
ment S4-25, 18 element £1-75. CHIMNEY 
MOUNTING ARRAYS o;'w MAST AND LASH- 
ING KIT. 7 element £4, 11 element £4-90. 14 
element £4>7S. 18 element £5-23. MAST MOUNT- 
ING arrays only 7 element £2*25. 11 element 
£2-75. 14 element £3-25. IS element £3-75. Com- 
plete assembly instruction* with every aerial, 
LOW LOSS coa-tial cable flp yd. KING TELE- 
BOOSTERS from £3*75. LABGEAR all band 
V.M.F.-U.H.F.-F.M. radio main* operated pre- 
amps £7-50, Stat* clearly channel number 
required on all orders. P.p. on all aerials SOp. 
Aces. 15p.- C.W.O. Mln. C.O.D. chaTge 25p. 

BBC-ITV-FM AERIALS 
BBC (band U Wall S;D £2. LOFT inverted "T" 
£1-25. EXTERNAL 'H' array only £3. ITV 
I Sand 81 5 element loft array £2-80, 7 element £3. 
COMBINED BBC-ITV luft 1 + 5 £2-75. 1 + 7 £3 ■BO. 
WALL AND CHIMNEY UNITS ALSO AVAIL- 
ABLE. Pre-ampa from B8-78. COMBINED U,H JT.- 
V.H.F. aerials 1+0 + 9 £4, 1 + 3 + 14 £4-60. 
1 + 7 + 14 £5. FM RADIO loft S/D £1. 3 element 
£3-25. 4 element t3-S0. Standard coaxial plugs 
9p. Coasial cable 5p yd. Outlet box 30p. P.p. 
all aerials 50p. Aces. 30p. C.W.O, 3£in. C.O.D. 
charge 23p. Send Op for fully illustrated lists. 

CALLERS WELCOMED 
OPEN ALL DAY SATURDAY 

K.V.A. ELECTRONICS 

40-41 Monarch Parade 

London Road, Mitcham, Surrey 

01-648 4884 



NEW VALVES 

Guaranteed and Tested 
24-HOUR SERVICE 



1R5 

1S5 

1T4 

384 

3V4 

0Y3GT 

6/30L2 

6AQ5 

6BW7 

8F1 

6F23 

GF25 

«SN7GT 

BULBS? 

30C15 

30C18 

30FS 

30FL1 

30FL14 

30L15 

30L17 

30F1 

30P1S 

30FL1 

30PL13 

30PL14 

DAF9I 

DAF96 

DCC90 



31 DF96 



DF91 



DK91 
DKB2 
DK9o 
DL92 
DL94 
DL96 
DY86 
DY87 
DYH02 
EABC8Q 
EB91 
EBC33 
EBFS9 
ECC81 
ECC82 
ECCS3 
ECC85 
ECF80 
ECF82 
ECH35 
ECHS1 
ECLS0 
._ ECL82 
63 ECL86 
EF39 
EF80 
EFSG 



EFS6 
EF89 
EFS1 
EF183 
EF184 
EL33 
EL37 
EL84 
BY61 
EY8H 
EZ80 
EZ81 
KT81 
KT68 
N78 
PC86 
FC88 
PC900 
PCC84 
PCC8B 
FCC 189 
PCF80 
PCF86 
29 1'CPflul 
29 F('Kwr> 
S5 PCF805 
38 I'I'LH2 
82PCL88 
881PCL84 



IPCL83 
1FCL86 
! PFL2fjn 
(PL36 
1PL81 
■54FL82 
-75JPL83 
-8SPLS4 



PLSfiM 
FLB04 
PY81 
PY82 
PY800 
PY801 
B19 
U25 
L*26 
U191 
U25I 
U329 
UBF8B 
27TTCCS5 
TJCH81 
UCLS2 
UCL83 
TJF89 
UL84 
TJY85 
Z77 



Postage on 1 valve 5p, on 2 or more valves 3p per valve 
extra. Any parcel Insured against damage In transit 3p 
extra. Office address, no callers. 

GERALD 
BERNARD 

83 OSBALDESTON ROAD 
STOKE NEWINCTON 
LONDON N.I 6 






DON'T BE CAUGHT OUT! 

Colour television is already here, but 
1971 is a big year for colour television 
with a number of single standard colour 

sets coming on to the market, engineers 
with a knowledge of colour television 
will obviously be in great demand. 

SO DON'T DELAY 

We have developed a colour television course 
geared for the service engineer which will 
enable him to tackle any problem in colour 
television. 

The course consists of 10 lessons on colour 
mixing. Pal colour system, colour 
receivers, decoders, IF circuits, time- 
bases, convergence, waveforms, set-up 
procedures, test equipment, fault find- 
ing, typical circuits. Fee for complete 

COUrse 10 gnS. Write for details without obligation to: 

DAYLIN ELECTRONICS 

(Dept. A) la Avebury Road 
SOUTHEND-ON-SEA 




REBUILT TUBES! 



YOU'RE 

SAFE 

WHEN YOU 

BUY FROM 

RE-VIEW! 



HERE IS WHAT YOU PAY: 

12m £4 75 21 in £7-25 

I4in £500 23in £8-50 

I5in £5-25 Twin Panel & Rimguard 

I71n £5-25 I9in £8 00 

I9in £5-87 23in £1050 

Cash or cheque with order, or cosh on delivery 

COLOUR TUBES AVAILABLE 

Discount for Trade 

■£ Each tube is rebuilt with a completely new gun 

assembly and the correct voltage heater. 
■jlr Each tube comes to you with a guarantee card 
covering it for two years against all but breakage. 
■^ Each tube is delivered free anywhere in the U.K. 

and insured on the journey. 
■^ Each tube is rebuilt with experience and know- 
how. We were amongst the very first to pioneer 
the technique of rebuilding television tubes. 

RE-VIEW ELECTRONIC TUBES 

237 London Rood, West Croydon, Surrey 
Tel. 01-689/7735 



IMF. COLOUR AND TELEVISION SPARES 

COLOUR DLI DELAY UNIT £3-85 p.p. 25p, LUMINANCE 
DELAY UNIT £1-35 p.p. I5p. PLESSEY SCAN COILS £5-75 
p.p. 35p, CONVERGENCE COILS £3-80 p.p. 25p, BLUE 
LATERAL £1-25 p.p. 9p, or Complete Set £10 p.p. 50p. 
MULLARD TYPE, SCAN COILS £3-50 p.p. 35p, CONVER 
GENCE COILS £1-75 p.p. 25p. LUMINANCE/CHRI 



PANEL £1 p.p. 25p. 



CE/CHR OMIN ANCE 
INTEGRATED TRANSISTORISED 



DECODER UNIT including Circuits £1-25 p.p. lOp. LLNE 
OUTPUT TRANSFORMER including EHT and FOCUS 
ASSEMBLY £3-50 p.p. 35p. (Shop customers onlv. assortment 
Colour Panels of various makes.) ALSO COLOUR TV CAMERA 
UNITS. 

COLOUR TV MONITOR PANELS Designed to highest BBC 
standards. PAL filter & delay £8-00, Chrominance £6-00, 
Luminance 34-50, Encoded Video Input £2-50 incL circuit, p.p. 30p. 
UHF 625 conversion kits and tuners available at reduced prices. 
Lists available, 

UHF Integrated transistd. 6 position push button tuners, leading 
British makers surplus £4>50 p.p. 35p. Transistd. IF panels 
(salvaged) £2-50 p.p. 25p. 

MURPHY 600/700 series UHF conversion kits in cabinet plinth 
assembly can be used as separate UHF receiver £7-50 pp 50p 
625 I K amplifier incl. 5 valves and circuit £3 p.p. 35p. 
SOBELL/GEC Dual 405/625 IF amp and o/p chassis inch circuit 
£1 -50 p.p. 30p. ULTRA 1980 C to 2384 625 IF amp & switch 
inch circuit £150 p.p. 30p. PHILIPS 625 P/C IF panel inch 
circuit £1 p.p. 25p. 

UHF tuners transistd. incl, S/M drive, knobs £3-95, or push- 
button £5-25. Valve type, cyldon £1-75 p.p. 25p Manv others 
EKCO/FERRANTI UHF tuner kit, incl. valves, slow motion 
dri%*e, knobs, leads, aerial panel £5 '50 p.p. 30p 
TV SIGNAL BOOSTER UNITS Latest PYE/LABGEAR all 
station LHF/VHF transistd. "Set back" mains operated £5-90 
UHF Masthead £4-25. Power Unit £3-25 pp.. 25p 
FIREBALL TUNERS Ferg., HMV, Marconi. New £1-90 p.p 25p 
PUSH BUTTON Plessy, Ekco. Ferranti £1-50 pp 25p 
TURRET TUNERS, AB Dual Standard Suitable Ferguson 
Baird, KB etc. 75p, Cyldon C 75p, Ferguson MT7 £2-75, GEC 
2018/9 £4-50, Pyc 110/510 min. incr*mental £2-90 p.p! 25p. 
LurKi- selection channel coils. 

LINE OUTPUT TRANSFORMERS. Popular types available 
brand new replacements, fully guar. A selection which can be 
supplied p.p. 25p. C.O.D. 25p. 



£3-50 
£4-00 
£4-50 
£4-50 



£3-95 
£3-75 



£3-75 
£4-00 
£3-75 



£3-50 
£3-50 



£2-50 



£2-50 

£3-25 
£3-25 
£4-50 
£2-25 

£3-75 



Bush TV75/86 . . 

Bush TV93/99 . . 

BUSH 141, 148, 

15KY 

EKCO 407/417 . . 

FERR. 1084/1092 £2-50 

Murphy 149, 

159, 15KV 

REG 10-6. 10-17 

REG 191, 192, 

17-18 

RGD 610, 7H . . 



MU RPHY 470 to 530 (oilfllted) . . £3-75 
MURPHY 849 to 939 .. .. £4-50 

PHILIPS 1768/2168 . . £4-50 

PHILIPS 17TG100 Range 
STELLA 1011/1029 
PHILIPS IGTG1 11/12 . . 

121 to 155 

PHILIPS 19TG170, 210 series 
B U S H T Y53 to 69 £1-75 105 to 135 £4 -50 
EKCO 221 to 331 (U25 or U26) £3-50 
FERRANTI 1001/19 (U25 or U26) £3.-50 
EKCO 342 to 304, FERRANTI 

1021 to 1065 £3-TS[RGD 619,' 620 

EKCO, FERRANTI 418, 1093 etc. £3'50 
DECCA DM 17. :;, I (70;l DR95, 

101/606 

FERG 305 to 436, 505 to 727 . . 
FERG, HMV, MARCONI, 
ULTRA, PHILCO 3600, 2600, 
4600, 6600, 1100, Jellvpot 
KB QV20, PVP20. VC1 to VC11 
MARCONI VT157 to 172 
GEC 302 to 346, £2-50, 448 to 452, £3-25 
GEC 454/6, 2000 series . . . . £4-50 

HMV 1865/9, 1870/6, 1890/1924 £3-75 
PYE CTM/CW series (printed 
circuit) 17/21, 17/S, 110 to 510, 
700, 830, 1, 2, 3, 11U to 48 . . 
PAM, IN VICT A equiv. LOPTS 

to above PYE 

PETO SCOTT 1410 to 1725 £1-75, 
733 to 738 

SOBELL/McMICHAEL TPS 173, 
180, T23, 24. 178, 278, SC24, 270, 
MP17, 18, M72, M74 
TPS 781, 279, SC34, 370, MP27, 

M75, 76, 93 

195, 282 to 288, 762, 763 

SO BELL 196/7, 1000 scries 

PHILCO 1010 to 1021 

ULTRA 1770 to 2834 

PRACTICAL TV 625 RECEIVER 

Integrated push button transistorised tuner 

Transistorised IF panel 

850 line output transformer 

850 field output transformer 

850 scan coils 



£2-50 

£2-50 



£2-50 

£2-50 



£2-50 

£2-50 



£2-50 

£2-50 
£2-50 



LOPT Inserts p.p. 15p 

Alba 655, 656 .. £1-75 

Bush 125 to 135 

(Round Tag 

Panel) . . . . £2-50 

Cossor 933 to 950 £1-75 

EkcoTP308 .. £1'75 

Emerson 700/711 £1-75 

KB, NF70, OV30, 

PV40, PVP20, 

QV10, 20, 30 

KB/RGD VCII 

Featherlight 

KB/RGD VC1-9 £1'75 

Murphv 849 to 

939 (Round Tag 

Panel) 

Philco 1030 series £1-75 

Philips 17TG100 

range 

Pye, VT4, VT7 . . 

RGD 017, 590 to 

619 

REG 10-4. 10-12 

to 192 .. .. £1-75 

Ultra 1770, 1780 £1-75 



£1-75 
£2-50 



£2-50 



£1-75 
£2-15 



£1-75 



£4-50 p.p. 25p 
£4-75 p.p. 25p 
£3-75 p.p. 25p 
£1-62 p.p. 15p 
£3 90 p.p. 25p 
(p.p. on complete set of 5 items 50p) 
VALVE BASES B9D for PL500 series and colonr 12ip p.p. 5p 
SCAN COILS PHILIPS, STELLA, COSSOR 110° models £2-85 

MANOR SUPPLIES 

172 WEST END LANE, LONDON, N.W.6 

[Heat W. Hampslead tube rtn ; 28, 59, 159 Bus Routes) 01-794 8751 

MAIL ORDER: 64 GQLDERS MANOR DRIVE, LONDON, N.W.11 



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Constructional 
A.M.S.E. 'Cii\ 
C. & G. Structural 
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Civil Engineering 
Building 

Air Conditioning 
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Surveying ■ 
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Decorating, 
Archi tea urc 
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General 
CJE.I 

Petroleum Tech. 
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Servicing. 
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Choose from 42 
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SO COULD YOU 

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These letters — and there are many more 
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Dept Bl Aldermaston 
Court, Reading RG7 4PF. 



Accredited by the Council for the 
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Have you had your copy of " Engineering Opportunities " ? 



The new edition of * 'ENGINEERING OPPOR- 
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to all who are anxious for a worthwhile post in 
Engineering. Frank, informative and completely 
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MIX 1 1. ENGINEERING 
(ifii. \1ech. Eng,- — Mainten- 
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VI postage for one year: To any part ot the World it- 13. u. ^ 



FIRST ... BEST 



PROVED and TESTED CIRCUITS 
QUALITY COMPONENTS and UNITS 



TRANSISTOR 




FIDELITY EQUIPMENT 



10 WATTS and 20 WATTS 



* MAINS UNITS 59'6 for one amplifier, 
or S? 6 to power 2 amplifiers. 



# Mono full function pre- 
amplifier with 8 input positions. 
Low noise, high quality and 
sensitivity. Gives 10 watts 
with one power amplifier or 
20 watts with two amplifiers. 
Size: 9 X 2j ;i 2in. 

P.P. 
2/- 
P,P, 
2 



•Jt 10 watt Power 
Amplifier 

(For IS 16 ohm 
SPEAKERS) 

P P 
BUILT £5.19.6 26 

(KIT £5.10.0 ££ 

■fc 10 watt Power 
Amplifier 

(For 3 to 5 ohm 
SPEAKERS) 

P P. 
BUILT £5.10.0 2/6 



P.P. 
2.6) 



(kit 99/6 
PREAMPLIFIER 



BUILT £5.10.0 

(kit 99/6 





•fc Dark Brown with Gold 
panel plate 8/6. 

• STERIO PREAMPLIFIER 

Two channel version of above. 
For use with two power ampli- 
fiers. For 10 -- 10 watts 
output. 
Size: 9 x 3i :■: I fin. 

£10.19.6 P 3/ P 6 



BUILT 

■jf Dark Brown 
Front Panel 1 2 '6. 



with Gold 



• MULTI-INPUT PREAMPLIFIER 

Simplified preamplifier for use with one or 
two power amplifiers, 8 inputs. 

E!S 65/- p.p. i* 

ic front Panel Plate 6/6, 

All the above preamplifiers can be used 

power amplifier requiring 250mV or full output. They can be operated 

with two S volt batteries in series or from the power amplifiers. 

All preamplifiers and power amplifiers are designed for high gain low 

distortion with excellent quality. 




iv valve 



CIRCUITS AND DETAILS ON REQUEST 



Demonstrations of above equipment and VHF FM Tuner can be heard 
during normal shop hours. All units are fully guaranteed. 



NEW 




TWO NEW PACKAGED TRANSISTOR 
QUALITY AMPLIFIERS 

6-Transistor printed circuit designs. Push-pull 
output for 3 to 5 ohm speakers. Can be battery operated. 
6mV into I Kohm sensitivity. Response 40 c/s to 
15 kc/s. 

Can be used with above preamplifiers for mono or 
stereo in any application requiring a low distortion 
low cost amplifier, 



4 WATT and 
I , WATT- 



OVERALL SIZES 21- x 2 

4 watt version operates 
from 12 to 18 volts. 

l| watt version from 9 
to 12 volts. 



I i inches. 



PRICE BUILT 79/6 
PRICE BUILT 65/- 



P.P. 

1/6 
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■* CIRCUITS AND DETAILS ON REQUEST * 



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For 12 volt positive earth or dry 
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After sales service and guarantee. 




the " roadster" 
total cost to build 

£8.19.6 p.p. 3 6 

#74 inch Hi-Flux-speakcr with 

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* CIRCUIT AND DETAILS 
ON REQUEST 



VHF TRANSISTOR FM TUNER * new low price * 



HIGH STABILITY — HIGH 
SENSITIVITY # 

Features S-Mullard transistors with 
4 diodes, compact printed circuit, 
high gain, low distortion, superhet 
design. Full tuning from 87/ IDS Mc/s 
with geared tuning. AVC and AFC. 
9 volt 9 mA operation, SO dB S/N, 
Output up to I volt audio. Easy to 
build and align. Overall size in cabinet 
3i .: 2i x 4in. All parts sold separately. 
After sales service and guarantee. 




CIRCUIT AND 
ON REQUEST 



DETAILS 



9 TOTAL COST WIIH FROM PANIl 

£6.19.6 PP2/6 

(Cabinet Assembly 20.'- extra) 



' CON V AIR' PUSH-BUTTON 
PORTABLE/CAR RADIO 

UNBEATABLE FOR PERFOR- 
MANCE AND DESIGN €> 

Printed circuit 6-Transistor 2-Diode 
superhet radio with full tuning cm 
medium and long wave bands. Quality 
push-pull output up to I watt. Attractive 
portable cabinet, size 10 7 x 3 jin, 
with horizontal slow motion tuning 
dial and push button wave change. 
Easy to build with superb performance. 
All p?rts sold separately. After sales 
service and guarantee. 
•fr CIRCUIT AND DETAILS 
ON REQUEST 




• tOUt COil OF All PARTS 

£7.19.6 p.p. 3/6 

(Batteries 6/- extra) 
-fc The finest portable available. 



BUILD A QUALITY TAPE RECORDER 

6-vafve printed circuit designs with 
Magic Eye ■ Collaro Studio 2-track or 
4-track decks. Portable cabinets with 8 >: 5in. 
speakers. Complete in every detail. 

TWO oiP.P- FOUR nn PP 

TRACK "Os/6 TRACK tJU8'6 

ir DETAIL LEAFLET ON REQUEST * 




SS-5*- MULTIMETERS 




BRAND NEW. 
FULLY GUARANTEED 



PT34 I Kohm "volt sensitivity 39 6 

H CABYMI 2 Kohm.volt sensitivity 49 6 
I THL33 2 Kohm/volt sensitivity 75/- 
(llluscrated) 
10 Kohm/vott sensitivity 79 '6 
20 Kohm'volc sensitivity 82 6 
20 Kohm/volt sensitivity £5.19.6 
30 Kohm/volt sensitivity £8.19.6 
30 Kohm/volt sensitivity £5.10.0 



EPI0K 

ITI2 

TP5S 

500 

EP30K 

EPS0K 



POST 
AND 
PACK- 
ING 
1,6 
ANY 
MODEL 



50 Kohm/volt sensitivity £8.10.0 



EPI00K 100 Kohm.volt sensitivity £9.19.6 



We can supply from stock most 
of the components and items 
specified on circuits published 
in this and other magazines. 
Quality parts at realistic prices. 
Let us quote for your circuit. 



300 

800 
500 



TRANSISTOR TYPES, 
DIODES AND 
RECTIFIERS 

VALVES AND TUBES 

QUARTZ CRYSTALS 



I LATEST CATALOGUE 

86 PAGES, 10" x 7}" 

fuffy detailed and illustrated. • 

Price 2 6 post paid. 

Latest 8 page valve, transistor and 



HENRY'S RADIO -LTD. 

303EDGWARERD., LONDON W2 



PADdington 1008,9 



I cr^taj^uppjement free on req uest. , pen Won, to Sot, 9-6. Than. I o'c/ocfc